target/linux/generic/backport-4.9/024-4-tcp-tsq-avoid-one-atomic-in-tcp_wfree.patch

   1 From a9b204d1564702b704ad6fe74f10a102c7b87ba3 Mon Sep 17 00:00:00 2001
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Sat, 3 Dec 2016 11:14:53 -0800
   4 Subject: [PATCH 04/10] tcp: tsq: avoid one atomic in tcp_wfree()
   5
   6 Under high load, tcp_wfree() has an atomic operation trying
   7 to schedule a tasklet over and over.
   8
   9 We can schedule it only if our per cpu list was empty.
  10
  11 Signed-off-by: Eric Dumazet <edumazet@google.com>
  12 Signed-off-by: David S. Miller <davem@davemloft.net>
  13 ---
  14  net/ipv4/tcp_output.c | 5 ++++-
  15  1 file changed, 4 insertions(+), 1 deletion(-)
  16
  17 --- a/net/ipv4/tcp_output.c
  18 +++ b/net/ipv4/tcp_output.c
  19 @@ -880,6 +880,7 @@ void tcp_wfree(struct sk_buff *skb)
  20
  21         for (oval = READ_ONCE(tp->tsq_flags);; oval = nval) {
  22                 struct tsq_tasklet *tsq;
  23 +               bool empty;
  24
  25                 if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
  26                         goto out;
  27 @@ -892,8 +893,10 @@ void tcp_wfree(struct sk_buff *skb)
  28                 /* queue this socket to tasklet queue */
  29                 local_irq_save(flags);
  30                 tsq = this_cpu_ptr(&tsq_tasklet);
  31 +               empty = list_empty(&tsq->head);
  32                 list_add(&tp->tsq_node, &tsq->head);
  33 -               tasklet_schedule(&tsq->tasklet);
  34 +               if (empty)
  35 +                       tasklet_schedule(&tsq->tasklet);
  36                 local_irq_restore(flags);
  37                 return;
  38         }