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Commit 1f4c6eb2 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

ipv6: factorize sk_wmem_alloc updates done by __ip6_append_data() 



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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 694aba69

net/ipv6/ip6_output.c

+12 −5
Original line number Diff line number Diff line
@@ -1259,6 +1259,7 @@ static int __ip6_append_data(struct sock *sk, 
	struct ipv6_txoptions *opt = v6_cork->opt;

	int csummode = CHECKSUM_NONE;

	unsigned int maxnonfragsize, headersize;

	unsigned int wmem_alloc_delta = 0;



	skb = skb_peek_tail(queue);

	if (!skb) {
@@ -1411,10 +1412,9 @@ static int __ip6_append_data(struct sock *sk, 
						(flags & MSG_DONTWAIT), &err);

			} else {

				skb = NULL;

				if (refcount_read(&sk->sk_wmem_alloc) <=

				if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=

				    2 * sk->sk_sndbuf)

					skb = sock_wmalloc(sk,

							   alloclen + hh_len, 1,

					skb = alloc_skb(alloclen + hh_len,

							sk->sk_allocation);

				if (unlikely(!skb))

					err = -ENOBUFS;
@@ -1474,6 +1474,11 @@ static int __ip6_append_data(struct sock *sk, 
			/*

			 * 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);

			continue;

		}
@@ -1520,12 +1525,13 @@ static int __ip6_append_data(struct sock *sk, 
			skb->len += copy;

			skb->data_len += copy;

			skb->truesize += copy;

			refcount_add(copy, &sk->sk_wmem_alloc);

			wmem_alloc_delta += copy;

		}

		offset += copy;

		length -= copy;

	}



	refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);

	return 0;



error_efault:
@@ -1533,6 +1539,7 @@ static int __ip6_append_data(struct sock *sk, 
error:

	cork->length -= length;

	IP6_INC_STATS(sock_net(sk), rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);

	refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);

	return err;

}