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tcp: tsq: add a shortcut in tcp_small_queue_check()

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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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-12-03 11:14:54 -08:00 committed by David S. Miller
parent a9b204d156
commit 75eefc6c59
1 changed files with 9 additions and 0 deletions
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9
net/ipv4/tcp_output.c
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@ -2091,6 +2091,15 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
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