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Date: Fri, 20 Dec 2013 17:56:52 -0500 (EST) From: David Miller <davem@...emloft.net> To: eric.dumazet@...il.com Cc: netdev@...r.kernel.org, willemb@...gle.com, ncardwell@...gle.com Subject: Re: [PATCH] tcp: autocork should not hold first packet in write queue From: Eric Dumazet <eric.dumazet@...il.com> Date: Tue, 17 Dec 2013 09:58:30 -0800 > From: Eric Dumazet <edumazet@...gle.com> > > 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) ... > Reported-by: Willem de Bruijn <willemb@...gle.com> > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > Fixes: f54b311142a9 ("tcp: auto corking") Applied, but please put "net-next" in the subject line next time. Thank you. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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