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authorEric Dumazet <edumazet@google.com>2013-12-17 09:58:30 -0800
committerDavid S. Miller <davem@davemloft.net>2013-12-20 17:56:25 -0500
commita181ceb501b31b4bf8812a5c84c716cc31d82c2d (patch)
tree8233fdcc125262b4985b26ff46d1c58bf2592d1a /drivers/net/ethernet
parenta792866ad2dafb8f272e4fdfb98a93fdbfff2277 (diff)
downloadlwn-a181ceb501b31b4bf8812a5c84c716cc31d82c2d.tar.gz
lwn-a181ceb501b31b4bf8812a5c84c716cc31d82c2d.zip
tcp: autocork should not hold first packet in write queue
Willem noticed a TCP_RR regression caused by TCP autocorking on a Mellanox test bed. MLX4_EN_TX_COAL_TIME is 16 us, which can be right above RTT between hosts. We can receive a ACK for a packet still in NIC TX ring buffer or in a softnet completion queue. Fix this by always pushing the skb if it is at the head of write queue. Also, as TX completion is lockless, it's safer to perform sk_wmem_alloc test after setting TSQ_THROTTLED. erd:~# MIB="MIN_LATENCY,MEAN_LATENCY,MAX_LATENCY,P99_LATENCY,STDDEV_LATENCY" erd:~# ./netperf -H remote -t TCP_RR -- -o $MIB | tail -n 1 (repeat 3 times) Before patch : 18,1049.87,41004,39631,6295.47 17,239.52,40804,48,2912.79 18,348.40,40877,54,3573.39 After patch : 18,22.84,4606,38,16.39 17,21.56,2871,36,13.51 17,22.46,2705,37,11.83 Reported-by: Willem de Bruijn <willemb@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Fixes: f54b311142a9 ("tcp: auto corking") Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/ethernet')
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