From 6ef30bdab8dab92939edbc964237b844efbe5946 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 13 Nov 2013 06:32:54 -0800 Subject: 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 Reported-by: Sujith Manoharan Reported-by: Arnaud Ebalard Tested-by: Sujith Manoharan Cc: Felix Fietkau Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp.c | 6 ------ 1 file changed, 6 deletions(-) (limited to 'net/ipv4/tcp.c') diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index c888abf5a72..ae15c18df88 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -807,12 +807,6 @@ static unsigned int tcp_xmit_size_goal(struct sock *sk, u32 mss_now, xmit_size_goal = min_t(u32, gso_size, sk->sk_gso_max_size - 1 - hlen); - /* TSQ : try to have at least two segments in flight - * (one in NIC TX ring, another in Qdisc) - */ - xmit_size_goal = min_t(u32, xmit_size_goal, - sysctl_tcp_limit_output_bytes >> 1); - xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal); /* We try hard to avoid divides here */ -- cgit v1.2.3-18-g5258