From 0a6b2a1dc2a2105f178255fe495eb914b09cb37a Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 19 Feb 2018 11:56:47 -0800 Subject: tcp: switch to GSO being always on Oleksandr Natalenko reported performance issues with BBR without FQ packet scheduler that were root caused to lack of SG and GSO/TSO on his configuration. In this mode, TCP internal pacing has to setup a high resolution timer for each MSS sent. We could implement in TCP a strategy similar to the one adopted in commit fefa569a9d4b ("net_sched: sch_fq: account for schedule/timers drifts") or decide to finally switch TCP stack to a GSO only mode. This has many benefits : 1) Most TCP developments are done with TSO in mind. 2) Less high-resolution timers needs to be armed for TCP-pacing 3) GSO can benefit of xmit_more hint 4) Receiver GRO is more effective (as if TSO was used for real on sender) -> Lower ACK traffic 5) Write queues have less overhead (one skb holds about 64KB of payload) 6) SACK coalescing just works. 7) rtx rb-tree contains less packets, SACK is cheaper. This patch implements the minimum patch, but we can remove some legacy code as follow ups. Tested: On 40Gbit link, one netperf -t TCP_STREAM BBR+fq: sg on: 26 Gbits/sec sg off: 15.7 Gbits/sec (was 2.3 Gbit before patch) BBR+pfifo_fast: sg on: 24.2 Gbits/sec sg off: 14.9 Gbits/sec (was 0.66 Gbit before patch !!! ) BBR+fq_codel: sg on: 24.4 Gbits/sec sg off: 15 Gbits/sec (was 0.66 Gbit before patch !!! ) Signed-off-by: Eric Dumazet Reported-by: Oleksandr Natalenko Signed-off-by: David S. Miller --- net/core/sock.c | 2 +- net/ipv4/tcp.c | 1 + 2 files changed, 2 insertions(+), 1 deletion(-) (limited to 'net') diff --git a/net/core/sock.c b/net/core/sock.c index a1fa4a548f1b..507d8c6c4319 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1777,7 +1777,7 @@ void sk_setup_caps(struct sock *sk, struct dst_entry *dst) u32 max_segs = 1; sk_dst_set(sk, dst); - sk->sk_route_caps = dst->dev->features; + sk->sk_route_caps = dst->dev->features | sk->sk_route_forced_caps; if (sk->sk_route_caps & NETIF_F_GSO) sk->sk_route_caps |= NETIF_F_GSO_SOFTWARE; sk->sk_route_caps &= ~sk->sk_route_nocaps; diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 48636aee23c3..4b46a2ae46e3 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -453,6 +453,7 @@ void tcp_init_sock(struct sock *sk) sk->sk_rcvbuf = sock_net(sk)->ipv4.sysctl_tcp_rmem[1]; sk_sockets_allocated_inc(sk); + sk->sk_route_forced_caps = NETIF_F_GSO; } EXPORT_SYMBOL(tcp_init_sock); -- cgit v1.2.3-59-g8ed1b