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When the driver needs to send new packets to the device, it always queues the new sk_buffs into an intermediate queue (send_pkt_queue) and schedules a worker (send_pkt_work) to then queue them into the virtqueue exposed to the device. This increases the chance of batching, but also introduces a lot of latency into the communication. So we can optimize this path by adding a fast path to be taken when there is no element in the intermediate queue, there is space available in the virtqueue, and no other process that is sending packets (tx_lock held). The following benchmarks were run to check improvements in latency and throughput. The test bed is a host with Intel i7-10700KF CPU @ 3.80GHz and L1 guest running on QEMU/KVM with vhost process and all vCPUs pinned individually to pCPUs. - Latency Tool: Fio version 3.37-56 Mode: pingpong (h-g-h) Test runs: 50 Runtime-per-test: 50s Type: SOCK_STREAM In the following fio benchmark (pingpong mode) the host sends a payload to the guest and waits for the same payload back. fio process pinned both inside the host and the guest system. Before: Linux 6.9.8 Payload 64B: 1st perc. overall 99th perc. Before 12.91 16.78 42.24 us After 9.77 13.57 39.17 us Payload 512B: 1st perc. overall 99th perc. Before 13.35 17.35 41.52 us After 10.25 14.11 39.58 us Payload 4K: 1st perc. overall 99th perc. Before 14.71 19.87 41.52 us After 10.51 14.96 40.81 us - Throughput Tool: iperf-vsock The size represents the buffer length (-l) to read/write P represents the number of parallel streams P=1 4K 64K 128K Before 6.87 29.3 29.5 Gb/s After 10.5 39.4 39.9 Gb/s P=2 4K 64K 128K Before 10.5 32.8 33.2 Gb/s After 17.8 47.7 48.5 Gb/s P=4 4K 64K 128K Before 12.7 33.6 34.2 Gb/s After 16.9 48.1 50.5 Gb/s The performance improvement is related to this optimization, I used a ebpf kretprobe on virtio_transport_send_skb to check that each packet was sent directly to the virtqueue Co-developed-by: Marco Pinna <marco.pinn95@gmail.com> Signed-off-by: Marco Pinna <marco.pinn95@gmail.com> Signed-off-by: Luigi Leonardi <luigi.leonardi@outlook.com> Message-Id: <20240730-pinna-v4-2-5c9179164db5@outlook.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> |
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| .. | ||
| af_vsock_tap.c | ||
| af_vsock.c | ||
| diag.c | ||
| hyperv_transport.c | ||
| Kconfig | ||
| Makefile | ||
| virtio_transport_common.c | ||
| virtio_transport.c | ||
| vmci_transport_notify_qstate.c | ||
| vmci_transport_notify.c | ||
| vmci_transport_notify.h | ||
| vmci_transport.c | ||
| vmci_transport.h | ||
| vsock_addr.c | ||
| vsock_bpf.c | ||
| vsock_loopback.c | ||