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tcp: allow for bigger reordering level

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While testing upcoming Yaogong patch (converting out of order queue
into an RB tree), I hit the max reordering level of linux TCP stack.

Reordering level was limited to 127 for no good reason, and some
network setups [1] can easily reach this limit and get limited
throughput.

Allow a new max limit of 300, and add a sysctl to allow admins to even
allow bigger (or lower) values if needed.

[1] Aggregation of links, per packet load balancing, fabrics not doing
 deep packet inspections, alternative TCP congestion modules...

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yaogong Wang <wygivan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2014-10-27 21:45:24 -07:00 committed by David S. Miller
parent 7aef06db0f
commit dca145ffaa
6 changed files with 23 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
Documentation/networking/bonding.txt
View File

@ -2230,11 +2230,8 @@ balance-rr: This mode is the only mode that will permit a single
It is possible to adjust TCP/IP's congestion limits by
altering the net.ipv4.tcp_reordering sysctl parameter. The
usual default value is 3, and the maximum useful value is 127.
For a four interface balance-rr bond, expect that a single
TCP/IP stream will utilize no more than approximately 2.3
interface's worth of throughput, even after adjusting
tcp_reordering.
usual default value is 3. But keep in mind TCP stack is able
to automatically increase this when it detects reorders.
Note that the fraction of packets that will be delivered out of
order is highly variable, and is unlikely to be zero. The level

10
Documentation/networking/ip-sysctl.txt
View File

@ -376,9 +376,17 @@ tcp_orphan_retries - INTEGER
may consume significant resources. Cf. tcp_max_orphans.
tcp_reordering - INTEGER
Maximal reordering of packets in a TCP stream.
Initial reordering level of packets in a TCP stream.
TCP stack can then dynamically adjust flow reordering level
between this initial value and tcp_max_reordering
Default: 3
tcp_max_reordering - INTEGER
Maximal reordering level of packets in a TCP stream.
300 is a fairly conservative value, but you might increase it
if paths are using per packet load balancing (like bonding rr mode)
Default: 300
tcp_retrans_collapse - BOOLEAN
Bug-to-bug compatibility with some broken printers.
On retransmit try to send bigger packets to work around bugs in

4
include/linux/tcp.h
View File

@ -204,10 +204,10 @@ struct tcp_sock {
u16 urg_data; /* Saved octet of OOB data and control flags */
u8 ecn_flags; /* ECN status bits. */
u8 reordering; /* Packet reordering metric. */
u8 keepalive_probes; /* num of allowed keep alive probes */
u32 reordering; /* Packet reordering metric. */
u32 snd_up; /* Urgent pointer */
u8 keepalive_probes; /* num of allowed keep alive probes */
/*
* Options received (usually on last packet, some only on SYN packets).
*/

4
include/net/tcp.h
View File

@ -70,9 +70,6 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
/* After receiving this amount of duplicate ACKs fast retransmit starts. */
#define TCP_FASTRETRANS_THRESH 3
/* Maximal reordering. */
#define TCP_MAX_REORDERING 127
/* Maximal number of ACKs sent quickly to accelerate slow-start. */
#define TCP_MAX_QUICKACKS 16U
@ -252,6 +249,7 @@ extern int sysctl_tcp_abort_on_overflow;
extern int sysctl_tcp_max_orphans;
extern int sysctl_tcp_fack;
extern int sysctl_tcp_reordering;
extern int sysctl_tcp_max_reordering;
extern int sysctl_tcp_dsack;
extern long sysctl_tcp_mem[3];
extern int sysctl_tcp_wmem[3];

7
net/ipv4/sysctl_net_ipv4.c
View File

@ -495,6 +495,13 @@ static struct ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
{
.procname = "tcp_max_reordering",
.data = &sysctl_tcp_max_reordering,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec
},
{
.procname = "tcp_dsack",
.data = &sysctl_tcp_dsack,

3
net/ipv4/tcp_input.c
View File

@ -81,6 +81,7 @@ int sysctl_tcp_window_scaling __read_mostly = 1;
int sysctl_tcp_sack __read_mostly = 1;
int sysctl_tcp_fack __read_mostly = 1;
int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
int sysctl_tcp_max_reordering __read_mostly = 300;
EXPORT_SYMBOL(sysctl_tcp_reordering);
int sysctl_tcp_dsack __read_mostly = 1;
int sysctl_tcp_app_win __read_mostly = 31;
@ -833,7 +834,7 @@ static void tcp_update_reordering(struct sock *sk, const int metric,
if (metric > tp->reordering) {
int mib_idx;
tp->reordering = min(TCP_MAX_REORDERING, metric);
tp->reordering = min(sysctl_tcp_max_reordering, metric);
/* This exciting event is worth to be remembered. 8) */
if (ts)