diff options
| author | Eric Dumazet <edumazet@google.com> | 2013-12-17 09:58:30 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2013-12-20 17:56:25 -0500 |
| commit | a181ceb501b31b4bf8812a5c84c716cc31d82c2d (patch) | |
| tree | 8233fdcc125262b4985b26ff46d1c58bf2592d1a /net/ipv4/tcp.c | |
| parent | a792866ad2dafb8f272e4fdfb98a93fdbfff2277 (diff) | |
| download | linux-rt-a181ceb501b31b4bf8812a5c84c716cc31d82c2d.tar.gz | |
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 'net/ipv4/tcp.c')
| -rw-r--r-- | net/ipv4/tcp.c | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 0ca87547becb..d099f9a055c6 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -622,19 +622,21 @@ static inline void tcp_mark_urg(struct tcp_sock *tp, int flags) } /* If a not yet filled skb is pushed, do not send it if - * we have packets in Qdisc or NIC queues : + * we have data packets in Qdisc or NIC queues : * Because TX completion will happen shortly, it gives a chance * to coalesce future sendmsg() payload into this skb, without * need for a timer, and with no latency trade off. * As packets containing data payload have a bigger truesize - * than pure acks (dataless) packets, the last check prevents - * autocorking if we only have an ACK in Qdisc/NIC queues. + * than pure acks (dataless) packets, the last checks prevent + * autocorking if we only have an ACK in Qdisc/NIC queues, + * or if TX completion was delayed after we processed ACK packet. */ static bool tcp_should_autocork(struct sock *sk, struct sk_buff *skb, int size_goal) { return skb->len < size_goal && sysctl_tcp_autocorking && + skb != tcp_write_queue_head(sk) && atomic_read(&sk->sk_wmem_alloc) > skb->truesize; } @@ -660,7 +662,11 @@ static void tcp_push(struct sock *sk, int flags, int mss_now, NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPAUTOCORKING); set_bit(TSQ_THROTTLED, &tp->tsq_flags); } - return; + /* It is possible TX completion already happened + * before we set TSQ_THROTTLED. + */ + if (atomic_read(&sk->sk_wmem_alloc) > skb->truesize) + return; } if (flags & MSG_MORE) |