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authorEric Dumazet <edumazet@google.com>2013-11-13 06:32:54 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-12-08 07:29:12 -0800
commitf4a5ec10024217be0a05f568eca5a93ff756df10 (patch)
treeecd2d1f28c4e6581248b9e221394fcfcd9734435 /Documentation
parentebee20ff2444c1b65885ab1869001922e0a1f969 (diff)
downloadlinux-linaro-stable-f4a5ec10024217be0a05f568eca5a93ff756df10.tar.gz
tcp: tsq: restore minimal amount of queueing
[ Upstream commit 98e09386c0ef4dfd48af7ba60ff908f0d525cdee ] After commit c9eeec26e32e ("tcp: TSQ can use a dynamic limit"), several users reported throughput regressions, notably on mvneta and wifi adapters. 802.11 AMPDU requires a fair amount of queueing to be effective. This patch partially reverts the change done in tcp_write_xmit() so that the minimal amount is sysctl_tcp_limit_output_bytes. It also remove the use of this sysctl while building skb stored in write queue, as TSO autosizing does the right thing anyway. Users with well behaving NICS and correct qdisc (like sch_fq), can then lower the default sysctl_tcp_limit_output_bytes value from 128KB to 8KB. This new usage of sysctl_tcp_limit_output_bytes permits each driver authors to check how their driver performs when/if the value is set to a minimum of 4KB. Normally, line rate for a single TCP flow should be possible, but some drivers rely on timers to perform TX completion and too long TX completion delays prevent reaching full throughput. Fixes: c9eeec26e32e ("tcp: TSQ can use a dynamic limit") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Sujith Manoharan <sujith@msujith.org> Reported-by: Arnaud Ebalard <arno@natisbad.org> Tested-by: Sujith Manoharan <sujith@msujith.org> Cc: Felix Fietkau <nbd@openwrt.org> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/networking/ip-sysctl.txt3
1 files changed, 0 insertions, 3 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index a46d78583ae1..7d8dc93fe2eb 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -588,9 +588,6 @@ tcp_limit_output_bytes - INTEGER
typical pfifo_fast qdiscs.
tcp_limit_output_bytes limits the number of bytes on qdisc
or device to reduce artificial RTT/cwnd and reduce bufferbloat.
- Note: For GSO/TSO enabled flows, we try to have at least two
- packets in flight. Reducing tcp_limit_output_bytes might also
- reduce the size of individual GSO packet (64KB being the max)
Default: 131072
tcp_challenge_ack_limit - INTEGER