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authorEric Dumazet2018-02-19 11:56:47 -0800
committerDavid S. Miller2018-02-21 14:24:13 -0500
commit0a6b2a1dc2a2105f178255fe495eb914b09cb37a (patch)
tree532480b47dccd07039b68b0fc813fedd313905f5 /scripts/ld-version.sh
parent960103ff8dd176511d3735d22c14fb0a5ce3183e (diff)
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 <edumazet@google.com> Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name> Signed-off-by: David S. Miller <davem@davemloft.net>
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