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ipv6: factorize sk_wmem_alloc updates done by __ip6_append_data()

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While testing my inet defrag changes, I found that the senders
could spend ~20% of cpu cycles in skb_set_owner_w() updating
sk->sk_wmem_alloc for every fragment they cook, competing
with TX completion of prior skbs possibly happening on another cpus.

The solution to this problem is to use alloc_skb() instead
of sock_wmalloc() and manually perform a single sk_wmem_alloc change.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2018-03-31 13:16:26 -07:00 committed by David S. Miller
parent 694aba690d
commit 1f4c6eb240
1 changed files with 12 additions and 5 deletions
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17
net/ipv6/ip6_output.c
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@ -1259,6 +1259,7 @@ static int __ip6_append_data(struct sock *sk,
struct ipv6_txoptions *opt = v6_cork->opt; struct ipv6_txoptions *opt = v6_cork->opt;
int csummode = CHECKSUM_NONE; int csummode = CHECKSUM_NONE;
unsigned int maxnonfragsize, headersize; unsigned int maxnonfragsize, headersize;
unsigned int wmem_alloc_delta = 0;
skb = skb_peek_tail(queue); skb = skb_peek_tail(queue);
if (!skb) { if (!skb) {
@ -1411,11 +1412,10 @@ alloc_new_skb:
(flags & MSG_DONTWAIT), &err); (flags & MSG_DONTWAIT), &err);
} else { } else {
skb = NULL; skb = NULL;
if (refcount_read(&sk->sk_wmem_alloc) <= if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=
2 * sk->sk_sndbuf) 2 * sk->sk_sndbuf)
skb = sock_wmalloc(sk, skb = alloc_skb(alloclen + hh_len,
alloclen + hh_len, 1, sk->sk_allocation);
sk->sk_allocation);
if (unlikely(!skb)) if (unlikely(!skb))
err = -ENOBUFS; err = -ENOBUFS;
} }
@ -1474,6 +1474,11 @@ alloc_new_skb:
/* /*
* Put the packet on the pending queue * Put the packet on the pending queue
*/ */
if (!skb->destructor) {
skb->destructor = sock_wfree;
skb->sk = sk;
wmem_alloc_delta += skb->truesize;
}
__skb_queue_tail(queue, skb); __skb_queue_tail(queue, skb);
continue; continue;
} }
@ -1520,12 +1525,13 @@ alloc_new_skb:
skb->len += copy; skb->len += copy;
skb->data_len += copy; skb->data_len += copy;
skb->truesize += copy; skb->truesize += copy;
refcount_add(copy, &sk->sk_wmem_alloc); wmem_alloc_delta += copy;
} }
offset += copy; offset += copy;
length -= copy; length -= copy;
} }
refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
return 0; return 0;
error_efault: error_efault:
@ -1533,6 +1539,7 @@ error_efault:
error: error:
cork->length -= length; cork->length -= length;
IP6_INC_STATS(sock_net(sk), rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS); IP6_INC_STATS(sock_net(sk), rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
return err; return err;
} }