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tcp: tsq: add shortcut in tcp_tasklet_func()

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Under high stress, I've seen tcp_tasklet_func() consuming
~700 usec, handling ~150 tcp sockets.

By setting TCP_TSQ_DEFERRED in tcp_wfree(), we give a chance
for other cpus/threads entering tcp_write_xmit() to grab it,
allowing tcp_tasklet_func() to skip sockets that already did
an xmit cycle.

In the future, we might give to ACK processing an increased
budget to reduce even more tcp_tasklet_func() amount of work.

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 11:14:52 -08:00 committed by David S. Miller
parent 408f0a6c21
commit b223feb9de
1 changed files with 12 additions and 10 deletions
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22
net/ipv4/tcp_output.c
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@ -767,19 +767,19 @@ static void tcp_tasklet_func(unsigned long data)
list_for_each_safe(q, n, &list) {
tp = list_entry(q, struct tcp_sock, tsq_node);
list_del(&tp->tsq_node);
clear_bit(TSQ_QUEUED, &tp->tsq_flags);
sk = (struct sock *)tp;
bh_lock_sock(sk);
if (!sock_owned_by_user(sk)) {
tcp_tsq_handler(sk);
} else {
/* defer the work to tcp_release_cb() */
set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
if (!sk->sk_lock.owned &&
test_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags)) {
bh_lock_sock(sk);
if (!sock_owned_by_user(sk)) {
clear_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
tcp_tsq_handler(sk);
}
bh_unlock_sock(sk);
}
bh_unlock_sock(sk);
clear_bit(TSQ_QUEUED, &tp->tsq_flags);
sk_free(sk);
}
}
@ -884,7 +884,7 @@ void tcp_wfree(struct sk_buff *skb)
if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
goto out;
nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED;
nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
nval = cmpxchg(&tp->tsq_flags, oval, nval);
if (nval != oval)
continue;
@ -2229,6 +2229,8 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
break;
if (test_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags))
clear_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
if (tcp_small_queue_check(sk, skb, 0))
break;