From 75eefc6c59fd2c5f1ab95a3a113c217237d12a31 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 3 Dec 2016 11:14:54 -0800 Subject: [PATCH 05/10] tcp: tsq: add a shortcut in tcp_small_queue_check() Always allow the two first skbs in write queue to be sent, regardless of sk_wmem_alloc/sk_pacing_rate values. This helps a lot in situations where TX completions are delayed either because of driver latencies or softirq latencies. Test is done with no cache line misses. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2142,6 +2142,15 @@ static bool tcp_small_queue_check(struct limit <<= factor; if (atomic_read(&sk->sk_wmem_alloc) > limit) { + /* Always send the 1st or 2nd skb in write queue. + * No need to wait for TX completion to call us back, + * after softirq/tasklet schedule. + * This helps when TX completions are delayed too much. + */ + if (skb == sk->sk_write_queue.next || + skb->prev == sk->sk_write_queue.next) + return false; + set_bit(TSQ_THROTTLED, &tcp_sk(sk)->tsq_flags); /* It is possible TX completion already happened * before we set TSQ_THROTTLED, so we must