2018-05-02 11:01:36 +00:00
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.. SPDX-License-Identifier: GPL-2.0
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======
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AF_XDP
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======
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Overview
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========
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AF_XDP is an address family that is optimized for high performance
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packet processing.
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This document assumes that the reader is familiar with BPF and XDP. If
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not, the Cilium project has an excellent reference guide at
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xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
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http://cilium.readthedocs.io/en/latest/bpf/.
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2018-05-02 11:01:36 +00:00
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Using the XDP_REDIRECT action from an XDP program, the program can
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redirect ingress frames to other XDP enabled netdevs, using the
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bpf_redirect_map() function. AF_XDP sockets enable the possibility for
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XDP programs to redirect frames to a memory buffer in a user-space
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application.
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An AF_XDP socket (XSK) is created with the normal socket()
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syscall. Associated with each XSK are two rings: the RX ring and the
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TX ring. A socket can receive packets on the RX ring and it can send
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packets on the TX ring. These rings are registered and sized with the
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setsockopts XDP_RX_RING and XDP_TX_RING, respectively. It is mandatory
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to have at least one of these rings for each socket. An RX or TX
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descriptor ring points to a data buffer in a memory area called a
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UMEM. RX and TX can share the same UMEM so that a packet does not have
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to be copied between RX and TX. Moreover, if a packet needs to be kept
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for a while due to a possible retransmit, the descriptor that points
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to that packet can be changed to point to another and reused right
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away. This again avoids copying data.
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xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
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The UMEM consists of a number of equally sized chunks. A descriptor in
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one of the rings references a frame by referencing its addr. The addr
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is simply an offset within the entire UMEM region. The user space
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allocates memory for this UMEM using whatever means it feels is most
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appropriate (malloc, mmap, huge pages, etc). This memory area is then
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registered with the kernel using the new setsockopt XDP_UMEM_REG. The
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UMEM also has two rings: the FILL ring and the COMPLETION ring. The
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2019-10-21 08:57:04 +00:00
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FILL ring is used by the application to send down addr for the kernel
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xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
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to fill in with RX packet data. References to these frames will then
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appear in the RX ring once each packet has been received. The
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2019-10-21 08:57:04 +00:00
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COMPLETION ring, on the other hand, contains frame addr that the
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xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
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kernel has transmitted completely and can now be used again by user
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space, for either TX or RX. Thus, the frame addrs appearing in the
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2019-10-21 08:57:04 +00:00
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COMPLETION ring are addrs that were previously transmitted using the
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xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
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TX ring. In summary, the RX and FILL rings are used for the RX path
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and the TX and COMPLETION rings are used for the TX path.
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2018-05-02 11:01:36 +00:00
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The socket is then finally bound with a bind() call to a device and a
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specific queue id on that device, and it is not until bind is
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completed that traffic starts to flow.
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The UMEM can be shared between processes, if desired. If a process
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wants to do this, it simply skips the registration of the UMEM and its
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corresponding two rings, sets the XDP_SHARED_UMEM flag in the bind
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call and submits the XSK of the process it would like to share UMEM
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with as well as its own newly created XSK socket. The new process will
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xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
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then receive frame addr references in its own RX ring that point to
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this shared UMEM. Note that since the ring structures are
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single-consumer / single-producer (for performance reasons), the new
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process has to create its own socket with associated RX and TX rings,
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since it cannot share this with the other process. This is also the
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reason that there is only one set of FILL and COMPLETION rings per
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UMEM. It is the responsibility of a single process to handle the UMEM.
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2018-05-02 11:01:36 +00:00
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How is then packets distributed from an XDP program to the XSKs? There
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is a BPF map called XSKMAP (or BPF_MAP_TYPE_XSKMAP in full). The
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user-space application can place an XSK at an arbitrary place in this
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map. The XDP program can then redirect a packet to a specific index in
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this map and at this point XDP validates that the XSK in that map was
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indeed bound to that device and ring number. If not, the packet is
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dropped. If the map is empty at that index, the packet is also
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dropped. This also means that it is currently mandatory to have an XDP
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program loaded (and one XSK in the XSKMAP) to be able to get any
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traffic to user space through the XSK.
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AF_XDP can operate in two different modes: XDP_SKB and XDP_DRV. If the
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driver does not have support for XDP, or XDP_SKB is explicitly chosen
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when loading the XDP program, XDP_SKB mode is employed that uses SKBs
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together with the generic XDP support and copies out the data to user
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space. A fallback mode that works for any network device. On the other
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hand, if the driver has support for XDP, it will be used by the AF_XDP
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code to provide better performance, but there is still a copy of the
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data into user space.
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Concepts
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========
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In order to use an AF_XDP socket, a number of associated objects need
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to be setup. These objects and their options are explained in the
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following sections.
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2019-10-21 08:57:04 +00:00
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For an overview on how AF_XDP works, you can also take a look at the
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Linux Plumbers paper from 2018 on the subject:
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http://vger.kernel.org/lpc_net2018_talks/lpc18_paper_af_xdp_perf-v2.pdf. Do
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NOT consult the paper from 2017 on "AF_PACKET v4", the first attempt
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at AF_XDP. Nearly everything changed since then. Jonathan Corbet has
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also written an excellent article on LWN, "Accelerating networking
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with AF_XDP". It can be found at https://lwn.net/Articles/750845/.
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UMEM
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----
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UMEM is a region of virtual contiguous memory, divided into
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equal-sized frames. An UMEM is associated to a netdev and a specific
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xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
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queue id of that netdev. It is created and configured (chunk size,
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headroom, start address and size) by using the XDP_UMEM_REG setsockopt
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system call. A UMEM is bound to a netdev and queue id, via the bind()
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system call.
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2018-05-02 11:01:36 +00:00
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An AF_XDP is socket linked to a single UMEM, but one UMEM can have
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multiple AF_XDP sockets. To share an UMEM created via one socket A,
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the next socket B can do this by setting the XDP_SHARED_UMEM flag in
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struct sockaddr_xdp member sxdp_flags, and passing the file descriptor
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of A to struct sockaddr_xdp member sxdp_shared_umem_fd.
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2019-10-21 08:57:04 +00:00
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The UMEM has two single-producer/single-consumer rings that are used
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to transfer ownership of UMEM frames between the kernel and the
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user-space application.
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Rings
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-----
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There are a four different kind of rings: FILL, COMPLETION, RX and
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TX. All rings are single-producer/single-consumer, so the user-space
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application need explicit synchronization of multiple
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processes/threads are reading/writing to them.
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The UMEM uses two rings: FILL and COMPLETION. Each socket associated
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with the UMEM must have an RX queue, TX queue or both. Say, that there
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is a setup with four sockets (all doing TX and RX). Then there will be
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one FILL ring, one COMPLETION ring, four TX rings and four RX rings.
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2018-05-02 11:01:36 +00:00
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The rings are head(producer)/tail(consumer) based rings. A producer
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writes the data ring at the index pointed out by struct xdp_ring
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producer member, and increasing the producer index. A consumer reads
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the data ring at the index pointed out by struct xdp_ring consumer
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member, and increasing the consumer index.
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The rings are configured and created via the _RING setsockopt system
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|
|
|
calls and mmapped to user-space using the appropriate offset to mmap()
|
|
|
|
(XDP_PGOFF_RX_RING, XDP_PGOFF_TX_RING, XDP_UMEM_PGOFF_FILL_RING and
|
|
|
|
XDP_UMEM_PGOFF_COMPLETION_RING).
|
|
|
|
|
|
|
|
The size of the rings need to be of size power of two.
|
|
|
|
|
|
|
|
UMEM Fill Ring
|
|
|
|
~~~~~~~~~~~~~~
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
The FILL ring is used to transfer ownership of UMEM frames from
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
user-space to kernel-space. The UMEM addrs are passed in the ring. As
|
|
|
|
an example, if the UMEM is 64k and each chunk is 4k, then the UMEM has
|
|
|
|
16 chunks and can pass addrs between 0 and 64k.
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
Frames passed to the kernel are used for the ingress path (RX rings).
|
|
|
|
|
2019-08-27 02:25:31 +00:00
|
|
|
The user application produces UMEM addrs to this ring. Note that, if
|
|
|
|
running the application with aligned chunk mode, the kernel will mask
|
|
|
|
the incoming addr. E.g. for a chunk size of 2k, the log2(2048) LSB of
|
|
|
|
the addr will be masked off, meaning that 2048, 2050 and 3000 refers
|
|
|
|
to the same chunk. If the user application is run in the unaligned
|
|
|
|
chunks mode, then the incoming addr will be left untouched.
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
|
2018-05-02 11:01:36 +00:00
|
|
|
|
2018-10-04 17:01:32 +00:00
|
|
|
UMEM Completion Ring
|
|
|
|
~~~~~~~~~~~~~~~~~~~~
|
2018-05-02 11:01:36 +00:00
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
The COMPLETION Ring is used transfer ownership of UMEM frames from
|
|
|
|
kernel-space to user-space. Just like the FILL ring, UMEM indices are
|
2018-05-02 11:01:36 +00:00
|
|
|
used.
|
|
|
|
|
|
|
|
Frames passed from the kernel to user-space are frames that has been
|
|
|
|
sent (TX ring) and can be used by user-space again.
|
|
|
|
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
The user application consumes UMEM addrs from this ring.
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
|
|
|
|
RX Ring
|
|
|
|
~~~~~~~
|
|
|
|
|
|
|
|
The RX ring is the receiving side of a socket. Each entry in the ring
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
is a struct xdp_desc descriptor. The descriptor contains UMEM offset
|
|
|
|
(addr) and the length of the data (len).
|
2018-05-02 11:01:36 +00:00
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
If no frames have been passed to kernel via the FILL ring, no
|
2018-05-02 11:01:36 +00:00
|
|
|
descriptors will (or can) appear on the RX ring.
|
|
|
|
|
|
|
|
The user application consumes struct xdp_desc descriptors from this
|
|
|
|
ring.
|
|
|
|
|
|
|
|
TX Ring
|
|
|
|
~~~~~~~
|
|
|
|
|
|
|
|
The TX ring is used to send frames. The struct xdp_desc descriptor is
|
|
|
|
filled (index, length and offset) and passed into the ring.
|
|
|
|
|
|
|
|
To start the transfer a sendmsg() system call is required. This might
|
|
|
|
be relaxed in the future.
|
|
|
|
|
|
|
|
The user application produces struct xdp_desc descriptors to this
|
|
|
|
ring.
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
Libbpf
|
|
|
|
======
|
|
|
|
|
|
|
|
Libbpf is a helper library for eBPF and XDP that makes using these
|
|
|
|
technologies a lot simpler. It also contains specific helper functions
|
|
|
|
in tools/lib/bpf/xsk.h for facilitating the use of AF_XDP. It
|
|
|
|
contains two types of functions: those that can be used to make the
|
|
|
|
setup of AF_XDP socket easier and ones that can be used in the data
|
|
|
|
plane to access the rings safely and quickly. To see an example on how
|
|
|
|
to use this API, please take a look at the sample application in
|
|
|
|
samples/bpf/xdpsock_usr.c which uses libbpf for both setup and data
|
|
|
|
plane operations.
|
|
|
|
|
|
|
|
We recommend that you use this library unless you have become a power
|
|
|
|
user. It will make your program a lot simpler.
|
|
|
|
|
2018-05-02 11:01:36 +00:00
|
|
|
XSKMAP / BPF_MAP_TYPE_XSKMAP
|
2019-10-21 08:57:04 +00:00
|
|
|
============================
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
On XDP side there is a BPF map type BPF_MAP_TYPE_XSKMAP (XSKMAP) that
|
|
|
|
is used in conjunction with bpf_redirect_map() to pass the ingress
|
|
|
|
frame to a socket.
|
|
|
|
|
|
|
|
The user application inserts the socket into the map, via the bpf()
|
|
|
|
system call.
|
|
|
|
|
|
|
|
Note that if an XDP program tries to redirect to a socket that does
|
|
|
|
not match the queue configuration and netdev, the frame will be
|
|
|
|
dropped. E.g. an AF_XDP socket is bound to netdev eth0 and
|
|
|
|
queue 17. Only the XDP program executing for eth0 and queue 17 will
|
|
|
|
successfully pass data to the socket. Please refer to the sample
|
|
|
|
application (samples/bpf/) in for an example.
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
Configuration Flags and Socket Options
|
|
|
|
======================================
|
|
|
|
|
|
|
|
These are the various configuration flags that can be used to control
|
|
|
|
and monitor the behavior of AF_XDP sockets.
|
|
|
|
|
2021-07-06 05:44:00 +00:00
|
|
|
XDP_COPY and XDP_ZEROCOPY bind flags
|
|
|
|
------------------------------------
|
2019-10-21 08:57:04 +00:00
|
|
|
|
|
|
|
When you bind to a socket, the kernel will first try to use zero-copy
|
|
|
|
copy. If zero-copy is not supported, it will fall back on using copy
|
|
|
|
mode, i.e. copying all packets out to user space. But if you would
|
|
|
|
like to force a certain mode, you can use the following flags. If you
|
|
|
|
pass the XDP_COPY flag to the bind call, the kernel will force the
|
|
|
|
socket into copy mode. If it cannot use copy mode, the bind call will
|
2021-07-06 05:44:00 +00:00
|
|
|
fail with an error. Conversely, the XDP_ZEROCOPY flag will force the
|
2019-10-21 08:57:04 +00:00
|
|
|
socket into zero-copy mode or fail.
|
|
|
|
|
|
|
|
XDP_SHARED_UMEM bind flag
|
|
|
|
-------------------------
|
|
|
|
|
2020-08-28 08:26:29 +00:00
|
|
|
This flag enables you to bind multiple sockets to the same UMEM. It
|
|
|
|
works on the same queue id, between queue ids and between
|
|
|
|
netdevs/devices. In this mode, each socket has their own RX and TX
|
|
|
|
rings as usual, but you are going to have one or more FILL and
|
|
|
|
COMPLETION ring pairs. You have to create one of these pairs per
|
|
|
|
unique netdev and queue id tuple that you bind to.
|
|
|
|
|
|
|
|
Starting with the case were we would like to share a UMEM between
|
|
|
|
sockets bound to the same netdev and queue id. The UMEM (tied to the
|
|
|
|
fist socket created) will only have a single FILL ring and a single
|
|
|
|
COMPLETION ring as there is only on unique netdev,queue_id tuple that
|
|
|
|
we have bound to. To use this mode, create the first socket and bind
|
|
|
|
it in the normal way. Create a second socket and create an RX and a TX
|
|
|
|
ring, or at least one of them, but no FILL or COMPLETION rings as the
|
|
|
|
ones from the first socket will be used. In the bind call, set he
|
2019-10-21 08:57:04 +00:00
|
|
|
XDP_SHARED_UMEM option and provide the initial socket's fd in the
|
|
|
|
sxdp_shared_umem_fd field. You can attach an arbitrary number of extra
|
|
|
|
sockets this way.
|
|
|
|
|
|
|
|
What socket will then a packet arrive on? This is decided by the XDP
|
|
|
|
program. Put all the sockets in the XSK_MAP and just indicate which
|
|
|
|
index in the array you would like to send each packet to. A simple
|
|
|
|
round-robin example of distributing packets is shown below:
|
|
|
|
|
|
|
|
.. code-block:: c
|
|
|
|
|
|
|
|
#include <linux/bpf.h>
|
|
|
|
#include "bpf_helpers.h"
|
|
|
|
|
|
|
|
#define MAX_SOCKS 16
|
|
|
|
|
|
|
|
struct {
|
2021-06-22 18:56:47 +00:00
|
|
|
__uint(type, BPF_MAP_TYPE_XSKMAP);
|
|
|
|
__uint(max_entries, MAX_SOCKS);
|
|
|
|
__uint(key_size, sizeof(int));
|
|
|
|
__uint(value_size, sizeof(int));
|
2019-10-21 08:57:04 +00:00
|
|
|
} xsks_map SEC(".maps");
|
|
|
|
|
|
|
|
static unsigned int rr;
|
|
|
|
|
|
|
|
SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
|
|
|
|
{
|
2021-06-22 18:56:47 +00:00
|
|
|
rr = (rr + 1) & (MAX_SOCKS - 1);
|
2019-10-21 08:57:04 +00:00
|
|
|
|
2021-06-22 18:56:47 +00:00
|
|
|
return bpf_redirect_map(&xsks_map, rr, XDP_DROP);
|
2019-10-21 08:57:04 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
Note, that since there is only a single set of FILL and COMPLETION
|
|
|
|
rings, and they are single producer, single consumer rings, you need
|
|
|
|
to make sure that multiple processes or threads do not use these rings
|
|
|
|
concurrently. There are no synchronization primitives in the
|
|
|
|
libbpf code that protects multiple users at this point in time.
|
|
|
|
|
2019-11-07 17:47:40 +00:00
|
|
|
Libbpf uses this mode if you create more than one socket tied to the
|
2020-08-28 08:26:29 +00:00
|
|
|
same UMEM. However, note that you need to supply the
|
2019-11-07 17:47:40 +00:00
|
|
|
XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD libbpf_flag with the
|
|
|
|
xsk_socket__create calls and load your own XDP program as there is no
|
|
|
|
built in one in libbpf that will route the traffic for you.
|
|
|
|
|
2020-08-28 08:26:29 +00:00
|
|
|
The second case is when you share a UMEM between sockets that are
|
|
|
|
bound to different queue ids and/or netdevs. In this case you have to
|
|
|
|
create one FILL ring and one COMPLETION ring for each unique
|
|
|
|
netdev,queue_id pair. Let us say you want to create two sockets bound
|
|
|
|
to two different queue ids on the same netdev. Create the first socket
|
|
|
|
and bind it in the normal way. Create a second socket and create an RX
|
|
|
|
and a TX ring, or at least one of them, and then one FILL and
|
|
|
|
COMPLETION ring for this socket. Then in the bind call, set he
|
|
|
|
XDP_SHARED_UMEM option and provide the initial socket's fd in the
|
|
|
|
sxdp_shared_umem_fd field as you registered the UMEM on that
|
|
|
|
socket. These two sockets will now share one and the same UMEM.
|
|
|
|
|
2024-06-04 12:29:26 +00:00
|
|
|
There is no need to supply an XDP program like the one in the previous
|
|
|
|
case where sockets were bound to the same queue id and
|
|
|
|
device. Instead, use the NIC's packet steering capabilities to steer
|
|
|
|
the packets to the right queue. In the previous example, there is only
|
|
|
|
one queue shared among sockets, so the NIC cannot do this steering. It
|
|
|
|
can only steer between queues.
|
|
|
|
|
|
|
|
In libbpf, you need to use the xsk_socket__create_shared() API as it
|
|
|
|
takes a reference to a FILL ring and a COMPLETION ring that will be
|
|
|
|
created for you and bound to the shared UMEM. You can use this
|
|
|
|
function for all the sockets you create, or you can use it for the
|
|
|
|
second and following ones and use xsk_socket__create() for the first
|
|
|
|
one. Both methods yield the same result.
|
2020-08-28 08:26:29 +00:00
|
|
|
|
|
|
|
Note that a UMEM can be shared between sockets on the same queue id
|
|
|
|
and device, as well as between queues on the same device and between
|
2024-06-04 12:29:26 +00:00
|
|
|
devices at the same time.
|
2020-08-28 08:26:29 +00:00
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
XDP_USE_NEED_WAKEUP bind flag
|
|
|
|
-----------------------------
|
|
|
|
|
|
|
|
This option adds support for a new flag called need_wakeup that is
|
|
|
|
present in the FILL ring and the TX ring, the rings for which user
|
|
|
|
space is a producer. When this option is set in the bind call, the
|
|
|
|
need_wakeup flag will be set if the kernel needs to be explicitly
|
|
|
|
woken up by a syscall to continue processing packets. If the flag is
|
|
|
|
zero, no syscall is needed.
|
|
|
|
|
|
|
|
If the flag is set on the FILL ring, the application needs to call
|
|
|
|
poll() to be able to continue to receive packets on the RX ring. This
|
|
|
|
can happen, for example, when the kernel has detected that there are no
|
|
|
|
more buffers on the FILL ring and no buffers left on the RX HW ring of
|
|
|
|
the NIC. In this case, interrupts are turned off as the NIC cannot
|
|
|
|
receive any packets (as there are no buffers to put them in), and the
|
|
|
|
need_wakeup flag is set so that user space can put buffers on the
|
|
|
|
FILL ring and then call poll() so that the kernel driver can put these
|
|
|
|
buffers on the HW ring and start to receive packets.
|
|
|
|
|
|
|
|
If the flag is set for the TX ring, it means that the application
|
|
|
|
needs to explicitly notify the kernel to send any packets put on the
|
|
|
|
TX ring. This can be accomplished either by a poll() call, as in the
|
|
|
|
RX path, or by calling sendto().
|
|
|
|
|
|
|
|
An example of how to use this flag can be found in
|
|
|
|
samples/bpf/xdpsock_user.c. An example with the use of libbpf helpers
|
|
|
|
would look like this for the TX path:
|
|
|
|
|
|
|
|
.. code-block:: c
|
|
|
|
|
|
|
|
if (xsk_ring_prod__needs_wakeup(&my_tx_ring))
|
2021-06-22 18:56:47 +00:00
|
|
|
sendto(xsk_socket__fd(xsk_handle), NULL, 0, MSG_DONTWAIT, NULL, 0);
|
2019-10-21 08:57:04 +00:00
|
|
|
|
|
|
|
I.e., only use the syscall if the flag is set.
|
|
|
|
|
|
|
|
We recommend that you always enable this mode as it usually leads to
|
|
|
|
better performance especially if you run the application and the
|
|
|
|
driver on the same core, but also if you use different cores for the
|
|
|
|
application and the kernel driver, as it reduces the number of
|
|
|
|
syscalls needed for the TX path.
|
|
|
|
|
|
|
|
XDP_{RX|TX|UMEM_FILL|UMEM_COMPLETION}_RING setsockopts
|
|
|
|
------------------------------------------------------
|
|
|
|
|
|
|
|
These setsockopts sets the number of descriptors that the RX, TX,
|
|
|
|
FILL, and COMPLETION rings respectively should have. It is mandatory
|
|
|
|
to set the size of at least one of the RX and TX rings. If you set
|
|
|
|
both, you will be able to both receive and send traffic from your
|
|
|
|
application, but if you only want to do one of them, you can save
|
|
|
|
resources by only setting up one of them. Both the FILL ring and the
|
2019-11-07 17:47:40 +00:00
|
|
|
COMPLETION ring are mandatory as you need to have a UMEM tied to your
|
|
|
|
socket. But if the XDP_SHARED_UMEM flag is used, any socket after the
|
|
|
|
first one does not have a UMEM and should in that case not have any
|
2020-08-28 08:26:29 +00:00
|
|
|
FILL or COMPLETION rings created as the ones from the shared UMEM will
|
2019-11-07 17:47:40 +00:00
|
|
|
be used. Note, that the rings are single-producer single-consumer, so
|
|
|
|
do not try to access them from multiple processes at the same
|
|
|
|
time. See the XDP_SHARED_UMEM section.
|
|
|
|
|
|
|
|
In libbpf, you can create Rx-only and Tx-only sockets by supplying
|
|
|
|
NULL to the rx and tx arguments, respectively, to the
|
|
|
|
xsk_socket__create function.
|
|
|
|
|
|
|
|
If you create a Tx-only socket, we recommend that you do not put any
|
|
|
|
packets on the fill ring. If you do this, drivers might think you are
|
|
|
|
going to receive something when you in fact will not, and this can
|
|
|
|
negatively impact performance.
|
2019-10-21 08:57:04 +00:00
|
|
|
|
|
|
|
XDP_UMEM_REG setsockopt
|
|
|
|
-----------------------
|
|
|
|
|
|
|
|
This setsockopt registers a UMEM to a socket. This is the area that
|
2023-01-29 23:10:48 +00:00
|
|
|
contain all the buffers that packet can reside in. The call takes a
|
2019-10-21 08:57:04 +00:00
|
|
|
pointer to the beginning of this area and the size of it. Moreover, it
|
|
|
|
also has parameter called chunk_size that is the size that the UMEM is
|
|
|
|
divided into. It can only be 2K or 4K at the moment. If you have an
|
|
|
|
UMEM area that is 128K and a chunk size of 2K, this means that you
|
|
|
|
will be able to hold a maximum of 128K / 2K = 64 packets in your UMEM
|
|
|
|
area and that your largest packet size can be 2K.
|
|
|
|
|
|
|
|
There is also an option to set the headroom of each single buffer in
|
|
|
|
the UMEM. If you set this to N bytes, it means that the packet will
|
|
|
|
start N bytes into the buffer leaving the first N bytes for the
|
|
|
|
application to use. The final option is the flags field, but it will
|
|
|
|
be dealt with in separate sections for each UMEM flag.
|
|
|
|
|
2023-07-03 17:53:29 +00:00
|
|
|
SO_BINDTODEVICE setsockopt
|
|
|
|
--------------------------
|
|
|
|
|
|
|
|
This is a generic SOL_SOCKET option that can be used to tie AF_XDP
|
|
|
|
socket to a particular network interface. It is useful when a socket
|
|
|
|
is created by a privileged process and passed to a non-privileged one.
|
|
|
|
Once the option is set, kernel will refuse attempts to bind that socket
|
|
|
|
to a different interface. Updating the value requires CAP_NET_RAW.
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
XDP_STATISTICS getsockopt
|
|
|
|
-------------------------
|
|
|
|
|
|
|
|
Gets drop statistics of a socket that can be useful for debug
|
|
|
|
purposes. The supported statistics are shown below:
|
|
|
|
|
|
|
|
.. code-block:: c
|
|
|
|
|
|
|
|
struct xdp_statistics {
|
2021-06-22 18:56:47 +00:00
|
|
|
__u64 rx_dropped; /* Dropped for reasons other than invalid desc */
|
|
|
|
__u64 rx_invalid_descs; /* Dropped due to invalid descriptor */
|
|
|
|
__u64 tx_invalid_descs; /* Dropped due to invalid descriptor */
|
2019-10-21 08:57:04 +00:00
|
|
|
};
|
|
|
|
|
|
|
|
XDP_OPTIONS getsockopt
|
|
|
|
----------------------
|
|
|
|
|
|
|
|
Gets options from an XDP socket. The only one supported so far is
|
|
|
|
XDP_OPTIONS_ZEROCOPY which tells you if zero-copy is on or not.
|
|
|
|
|
2023-07-19 13:24:14 +00:00
|
|
|
Multi-Buffer Support
|
|
|
|
====================
|
|
|
|
|
|
|
|
With multi-buffer support, programs using AF_XDP sockets can receive
|
|
|
|
and transmit packets consisting of multiple buffers both in copy and
|
|
|
|
zero-copy mode. For example, a packet can consist of two
|
|
|
|
frames/buffers, one with the header and the other one with the data,
|
|
|
|
or a 9K Ethernet jumbo frame can be constructed by chaining together
|
|
|
|
three 4K frames.
|
|
|
|
|
|
|
|
Some definitions:
|
|
|
|
|
|
|
|
* A packet consists of one or more frames
|
|
|
|
|
|
|
|
* A descriptor in one of the AF_XDP rings always refers to a single
|
|
|
|
frame. In the case the packet consists of a single frame, the
|
|
|
|
descriptor refers to the whole packet.
|
|
|
|
|
|
|
|
To enable multi-buffer support for an AF_XDP socket, use the new bind
|
|
|
|
flag XDP_USE_SG. If this is not provided, all multi-buffer packets
|
|
|
|
will be dropped just as before. Note that the XDP program loaded also
|
|
|
|
needs to be in multi-buffer mode. This can be accomplished by using
|
|
|
|
"xdp.frags" as the section name of the XDP program used.
|
|
|
|
|
|
|
|
To represent a packet consisting of multiple frames, a new flag called
|
|
|
|
XDP_PKT_CONTD is introduced in the options field of the Rx and Tx
|
|
|
|
descriptors. If it is true (1) the packet continues with the next
|
|
|
|
descriptor and if it is false (0) it means this is the last descriptor
|
|
|
|
of the packet. Why the reverse logic of end-of-packet (eop) flag found
|
|
|
|
in many NICs? Just to preserve compatibility with non-multi-buffer
|
|
|
|
applications that have this bit set to false for all packets on Rx,
|
|
|
|
and the apps set the options field to zero for Tx, as anything else
|
|
|
|
will be treated as an invalid descriptor.
|
|
|
|
|
|
|
|
These are the semantics for producing packets onto AF_XDP Tx ring
|
|
|
|
consisting of multiple frames:
|
|
|
|
|
|
|
|
* When an invalid descriptor is found, all the other
|
|
|
|
descriptors/frames of this packet are marked as invalid and not
|
|
|
|
completed. The next descriptor is treated as the start of a new
|
|
|
|
packet, even if this was not the intent (because we cannot guess
|
|
|
|
the intent). As before, if your program is producing invalid
|
|
|
|
descriptors you have a bug that must be fixed.
|
|
|
|
|
|
|
|
* Zero length descriptors are treated as invalid descriptors.
|
|
|
|
|
|
|
|
* For copy mode, the maximum supported number of frames in a packet is
|
|
|
|
equal to CONFIG_MAX_SKB_FRAGS + 1. If it is exceeded, all
|
|
|
|
descriptors accumulated so far are dropped and treated as
|
|
|
|
invalid. To produce an application that will work on any system
|
|
|
|
regardless of this config setting, limit the number of frags to 18,
|
|
|
|
as the minimum value of the config is 17.
|
|
|
|
|
|
|
|
* For zero-copy mode, the limit is up to what the NIC HW
|
|
|
|
supports. Usually at least five on the NICs we have checked. We
|
|
|
|
consciously chose to not enforce a rigid limit (such as
|
|
|
|
CONFIG_MAX_SKB_FRAGS + 1) for zero-copy mode, as it would have
|
|
|
|
resulted in copy actions under the hood to fit into what limit the
|
|
|
|
NIC supports. Kind of defeats the purpose of zero-copy mode. How to
|
|
|
|
probe for this limit is explained in the "probe for multi-buffer
|
|
|
|
support" section.
|
|
|
|
|
|
|
|
On the Rx path in copy-mode, the xsk core copies the XDP data into
|
|
|
|
multiple descriptors, if needed, and sets the XDP_PKT_CONTD flag as
|
|
|
|
detailed before. Zero-copy mode works the same, though the data is not
|
|
|
|
copied. When the application gets a descriptor with the XDP_PKT_CONTD
|
|
|
|
flag set to one, it means that the packet consists of multiple buffers
|
|
|
|
and it continues with the next buffer in the following
|
|
|
|
descriptor. When a descriptor with XDP_PKT_CONTD == 0 is received, it
|
|
|
|
means that this is the last buffer of the packet. AF_XDP guarantees
|
|
|
|
that only a complete packet (all frames in the packet) is sent to the
|
|
|
|
application. If there is not enough space in the AF_XDP Rx ring, all
|
|
|
|
frames of the packet will be dropped.
|
|
|
|
|
|
|
|
If application reads a batch of descriptors, using for example the libxdp
|
|
|
|
interfaces, it is not guaranteed that the batch will end with a full
|
|
|
|
packet. It might end in the middle of a packet and the rest of the
|
|
|
|
buffers of that packet will arrive at the beginning of the next batch,
|
|
|
|
since the libxdp interface does not read the whole ring (unless you
|
|
|
|
have an enormous batch size or a very small ring size).
|
|
|
|
|
|
|
|
An example program each for Rx and Tx multi-buffer support can be found
|
|
|
|
later in this document.
|
|
|
|
|
2018-05-02 11:01:36 +00:00
|
|
|
Usage
|
2023-07-19 13:24:14 +00:00
|
|
|
-----
|
2018-05-02 11:01:36 +00:00
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
In order to use AF_XDP sockets two parts are needed. The
|
2018-05-02 11:01:36 +00:00
|
|
|
user-space application and the XDP program. For a complete setup and
|
|
|
|
usage example, please refer to the sample application. The user-space
|
2019-06-21 20:13:10 +00:00
|
|
|
side is xdpsock_user.c and the XDP side is part of libbpf.
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
The XDP code sample included in tools/lib/bpf/xsk.c is the following:
|
|
|
|
|
|
|
|
.. code-block:: c
|
2019-06-21 20:13:10 +00:00
|
|
|
|
|
|
|
SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
|
|
|
|
{
|
|
|
|
int index = ctx->rx_queue_index;
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
// A set entry here means that the corresponding queue_id
|
2019-06-21 20:13:10 +00:00
|
|
|
// has an active AF_XDP socket bound to it.
|
|
|
|
if (bpf_map_lookup_elem(&xsks_map, &index))
|
|
|
|
return bpf_redirect_map(&xsks_map, index, 0);
|
|
|
|
|
|
|
|
return XDP_PASS;
|
|
|
|
}
|
2018-05-02 11:01:36 +00:00
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
A simple but not so performance ring dequeue and enqueue could look
|
|
|
|
like this:
|
|
|
|
|
|
|
|
.. code-block:: c
|
2018-05-02 11:01:36 +00:00
|
|
|
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
// struct xdp_rxtx_ring {
|
2021-06-22 18:56:47 +00:00
|
|
|
// __u32 *producer;
|
|
|
|
// __u32 *consumer;
|
|
|
|
// struct xdp_desc *desc;
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
// };
|
|
|
|
|
|
|
|
// struct xdp_umem_ring {
|
2021-06-22 18:56:47 +00:00
|
|
|
// __u32 *producer;
|
|
|
|
// __u32 *consumer;
|
|
|
|
// __u64 *desc;
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
// };
|
|
|
|
|
2018-05-02 11:01:36 +00:00
|
|
|
// typedef struct xdp_rxtx_ring RING;
|
|
|
|
// typedef struct xdp_umem_ring RING;
|
|
|
|
|
|
|
|
// typedef struct xdp_desc RING_TYPE;
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
// typedef __u64 RING_TYPE;
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
int dequeue_one(RING *ring, RING_TYPE *item)
|
|
|
|
{
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
__u32 entries = *ring->producer - *ring->consumer;
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
if (entries == 0)
|
|
|
|
return -1;
|
|
|
|
|
|
|
|
// read-barrier!
|
|
|
|
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
*item = ring->desc[*ring->consumer & (RING_SIZE - 1)];
|
|
|
|
(*ring->consumer)++;
|
2018-05-02 11:01:36 +00:00
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
|
|
|
int enqueue_one(RING *ring, const RING_TYPE *item)
|
|
|
|
{
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
u32 free_entries = RING_SIZE - (*ring->producer - *ring->consumer);
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
if (free_entries == 0)
|
|
|
|
return -1;
|
|
|
|
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
ring->desc[*ring->producer & (RING_SIZE - 1)] = *item;
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
// write-barrier!
|
|
|
|
|
xsk: new descriptor addressing scheme
Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data. Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).
By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.
In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.
In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.
We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.
To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.
On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.
Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.
This commit changes the uapi of AF_XDP sockets, and updates the
documentation.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2018-06-04 11:57:13 +00:00
|
|
|
(*ring->producer)++;
|
2018-05-02 11:01:36 +00:00
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
But please use the libbpf functions as they are optimized and ready to
|
|
|
|
use. Will make your life easier.
|
2018-05-02 11:01:36 +00:00
|
|
|
|
2023-07-19 13:24:14 +00:00
|
|
|
Usage Multi-Buffer Rx
|
|
|
|
---------------------
|
|
|
|
|
|
|
|
Here is a simple Rx path pseudo-code example (using libxdp interfaces
|
|
|
|
for simplicity). Error paths have been excluded to keep it short:
|
|
|
|
|
|
|
|
.. code-block:: c
|
|
|
|
|
|
|
|
void rx_packets(struct xsk_socket_info *xsk)
|
|
|
|
{
|
|
|
|
static bool new_packet = true;
|
|
|
|
u32 idx_rx = 0, idx_fq = 0;
|
|
|
|
static char *pkt;
|
|
|
|
|
|
|
|
int rcvd = xsk_ring_cons__peek(&xsk->rx, opt_batch_size, &idx_rx);
|
|
|
|
|
|
|
|
xsk_ring_prod__reserve(&xsk->umem->fq, rcvd, &idx_fq);
|
|
|
|
|
|
|
|
for (int i = 0; i < rcvd; i++) {
|
|
|
|
struct xdp_desc *desc = xsk_ring_cons__rx_desc(&xsk->rx, idx_rx++);
|
|
|
|
char *frag = xsk_umem__get_data(xsk->umem->buffer, desc->addr);
|
|
|
|
bool eop = !(desc->options & XDP_PKT_CONTD);
|
|
|
|
|
|
|
|
if (new_packet)
|
|
|
|
pkt = frag;
|
|
|
|
else
|
|
|
|
add_frag_to_pkt(pkt, frag);
|
|
|
|
|
|
|
|
if (eop)
|
|
|
|
process_pkt(pkt);
|
|
|
|
|
|
|
|
new_packet = eop;
|
|
|
|
|
|
|
|
*xsk_ring_prod__fill_addr(&xsk->umem->fq, idx_fq++) = desc->addr;
|
|
|
|
}
|
|
|
|
|
|
|
|
xsk_ring_prod__submit(&xsk->umem->fq, rcvd);
|
|
|
|
xsk_ring_cons__release(&xsk->rx, rcvd);
|
|
|
|
}
|
|
|
|
|
|
|
|
Usage Multi-Buffer Tx
|
|
|
|
---------------------
|
|
|
|
|
|
|
|
Here is an example Tx path pseudo-code (using libxdp interfaces for
|
|
|
|
simplicity) ignoring that the umem is finite in size, and that we
|
|
|
|
eventually will run out of packets to send. Also assumes pkts.addr
|
|
|
|
points to a valid location in the umem.
|
|
|
|
|
|
|
|
.. code-block:: c
|
|
|
|
|
|
|
|
void tx_packets(struct xsk_socket_info *xsk, struct pkt *pkts,
|
|
|
|
int batch_size)
|
|
|
|
{
|
|
|
|
u32 idx, i, pkt_nb = 0;
|
|
|
|
|
|
|
|
xsk_ring_prod__reserve(&xsk->tx, batch_size, &idx);
|
|
|
|
|
|
|
|
for (i = 0; i < batch_size;) {
|
|
|
|
u64 addr = pkts[pkt_nb].addr;
|
|
|
|
u32 len = pkts[pkt_nb].size;
|
|
|
|
|
|
|
|
do {
|
|
|
|
struct xdp_desc *tx_desc;
|
|
|
|
|
|
|
|
tx_desc = xsk_ring_prod__tx_desc(&xsk->tx, idx + i++);
|
|
|
|
tx_desc->addr = addr;
|
|
|
|
|
|
|
|
if (len > xsk_frame_size) {
|
|
|
|
tx_desc->len = xsk_frame_size;
|
|
|
|
tx_desc->options = XDP_PKT_CONTD;
|
|
|
|
} else {
|
|
|
|
tx_desc->len = len;
|
|
|
|
tx_desc->options = 0;
|
|
|
|
pkt_nb++;
|
|
|
|
}
|
|
|
|
len -= tx_desc->len;
|
|
|
|
addr += xsk_frame_size;
|
|
|
|
|
|
|
|
if (i == batch_size) {
|
|
|
|
/* Remember len, addr, pkt_nb for next iteration.
|
|
|
|
* Skipped for simplicity.
|
|
|
|
*/
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
} while (len);
|
|
|
|
}
|
|
|
|
|
|
|
|
xsk_ring_prod__submit(&xsk->tx, i);
|
|
|
|
}
|
|
|
|
|
|
|
|
Probing for Multi-Buffer Support
|
|
|
|
--------------------------------
|
|
|
|
|
|
|
|
To discover if a driver supports multi-buffer AF_XDP in SKB or DRV
|
|
|
|
mode, use the XDP_FEATURES feature of netlink in linux/netdev.h to
|
|
|
|
query for NETDEV_XDP_ACT_RX_SG support. This is the same flag as for
|
|
|
|
querying for XDP multi-buffer support. If XDP supports multi-buffer in
|
|
|
|
a driver, then AF_XDP will also support that in SKB and DRV mode.
|
|
|
|
|
|
|
|
To discover if a driver supports multi-buffer AF_XDP in zero-copy
|
|
|
|
mode, use XDP_FEATURES and first check the NETDEV_XDP_ACT_XSK_ZEROCOPY
|
|
|
|
flag. If it is set, it means that at least zero-copy is supported and
|
|
|
|
you should go and check the netlink attribute
|
|
|
|
NETDEV_A_DEV_XDP_ZC_MAX_SEGS in linux/netdev.h. An unsigned integer
|
|
|
|
value will be returned stating the max number of frags that are
|
|
|
|
supported by this device in zero-copy mode. These are the possible
|
|
|
|
return values:
|
|
|
|
|
|
|
|
1: Multi-buffer for zero-copy is not supported by this device, as max
|
|
|
|
one fragment supported means that multi-buffer is not possible.
|
|
|
|
|
|
|
|
>=2: Multi-buffer is supported in zero-copy mode for this device. The
|
|
|
|
returned number signifies the max number of frags supported.
|
|
|
|
|
|
|
|
For an example on how these are used through libbpf, please take a
|
|
|
|
look at tools/testing/selftests/bpf/xskxceiver.c.
|
|
|
|
|
|
|
|
Multi-Buffer Support for Zero-Copy Drivers
|
|
|
|
------------------------------------------
|
|
|
|
|
|
|
|
Zero-copy drivers usually use the batched APIs for Rx and Tx
|
|
|
|
processing. Note that the Tx batch API guarantees that it will provide
|
|
|
|
a batch of Tx descriptors that ends with full packet at the end. This
|
|
|
|
to facilitate extending a zero-copy driver with multi-buffer support.
|
|
|
|
|
2018-05-02 11:01:36 +00:00
|
|
|
Sample application
|
|
|
|
==================
|
|
|
|
|
|
|
|
There is a xdpsock benchmarking/test application included that
|
2019-10-21 08:57:04 +00:00
|
|
|
demonstrates how to use AF_XDP sockets with private UMEMs. Say that
|
|
|
|
you would like your UDP traffic from port 4242 to end up in queue 16,
|
|
|
|
that we will enable AF_XDP on. Here, we use ethtool for this::
|
2018-05-02 11:01:36 +00:00
|
|
|
|
|
|
|
ethtool -N p3p2 rx-flow-hash udp4 fn
|
|
|
|
ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \
|
|
|
|
action 16
|
|
|
|
|
|
|
|
Running the rxdrop benchmark in XDP_DRV mode can then be done
|
|
|
|
using::
|
|
|
|
|
|
|
|
samples/bpf/xdpsock -i p3p2 -q 16 -r -N
|
|
|
|
|
|
|
|
For XDP_SKB mode, use the switch "-S" instead of "-N" and all options
|
|
|
|
can be displayed with "-h", as usual.
|
|
|
|
|
2019-10-21 08:57:04 +00:00
|
|
|
This sample application uses libbpf to make the setup and usage of
|
|
|
|
AF_XDP simpler. If you want to know how the raw uapi of AF_XDP is
|
|
|
|
really used to make something more advanced, take a look at the libbpf
|
|
|
|
code in tools/lib/bpf/xsk.[ch].
|
|
|
|
|
2019-02-21 09:21:28 +00:00
|
|
|
FAQ
|
|
|
|
=======
|
|
|
|
|
|
|
|
Q: I am not seeing any traffic on the socket. What am I doing wrong?
|
|
|
|
|
|
|
|
A: When a netdev of a physical NIC is initialized, Linux usually
|
2019-10-21 08:57:04 +00:00
|
|
|
allocates one RX and TX queue pair per core. So on a 8 core system,
|
2019-02-21 09:21:28 +00:00
|
|
|
queue ids 0 to 7 will be allocated, one per core. In the AF_XDP
|
|
|
|
bind call or the xsk_socket__create libbpf function call, you
|
|
|
|
specify a specific queue id to bind to and it is only the traffic
|
|
|
|
towards that queue you are going to get on you socket. So in the
|
|
|
|
example above, if you bind to queue 0, you are NOT going to get any
|
|
|
|
traffic that is distributed to queues 1 through 7. If you are
|
|
|
|
lucky, you will see the traffic, but usually it will end up on one
|
|
|
|
of the queues you have not bound to.
|
|
|
|
|
|
|
|
There are a number of ways to solve the problem of getting the
|
|
|
|
traffic you want to the queue id you bound to. If you want to see
|
|
|
|
all the traffic, you can force the netdev to only have 1 queue, queue
|
|
|
|
id 0, and then bind to queue 0. You can use ethtool to do this::
|
|
|
|
|
2019-05-20 21:22:25 +00:00
|
|
|
sudo ethtool -L <interface> combined 1
|
2019-02-21 09:21:28 +00:00
|
|
|
|
|
|
|
If you want to only see part of the traffic, you can program the
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NIC through ethtool to filter out your traffic to a single queue id
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that you can bind your XDP socket to. Here is one example in which
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UDP traffic to and from port 4242 are sent to queue 2::
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2019-05-20 21:22:25 +00:00
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sudo ethtool -N <interface> rx-flow-hash udp4 fn
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sudo ethtool -N <interface> flow-type udp4 src-port 4242 dst-port \
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4242 action 2
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2019-02-21 09:21:28 +00:00
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2019-10-21 08:57:04 +00:00
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A number of other ways are possible all up to the capabilities of
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2019-02-21 09:21:28 +00:00
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the NIC you have.
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2023-01-29 23:10:48 +00:00
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Q: Can I use the XSKMAP to implement a switch between different umems
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2019-10-21 08:57:04 +00:00
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in copy mode?
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A: The short answer is no, that is not supported at the moment. The
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XSKMAP can only be used to switch traffic coming in on queue id X
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to sockets bound to the same queue id X. The XSKMAP can contain
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sockets bound to different queue ids, for example X and Y, but only
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traffic goming in from queue id Y can be directed to sockets bound
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to the same queue id Y. In zero-copy mode, you should use the
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switch, or other distribution mechanism, in your NIC to direct
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traffic to the correct queue id and socket.
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2020-08-28 08:26:29 +00:00
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Q: My packets are sometimes corrupted. What is wrong?
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A: Care has to be taken not to feed the same buffer in the UMEM into
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more than one ring at the same time. If you for example feed the
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same buffer into the FILL ring and the TX ring at the same time, the
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NIC might receive data into the buffer at the same time it is
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sending it. This will cause some packets to become corrupted. Same
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thing goes for feeding the same buffer into the FILL rings
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belonging to different queue ids or netdevs bound with the
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XDP_SHARED_UMEM flag.
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2018-05-02 11:01:36 +00:00
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Credits
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=======
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- Björn Töpel (AF_XDP core)
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- Magnus Karlsson (AF_XDP core)
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- Alexander Duyck
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- Alexei Starovoitov
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- Daniel Borkmann
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- Jesper Dangaard Brouer
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- John Fastabend
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- Jonathan Corbet (LWN coverage)
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- Michael S. Tsirkin
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- Qi Z Zhang
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- Willem de Bruijn
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