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Commit 694aba69 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

ipv4: factorize sk_wmem_alloc updates done by __ip_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.

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

Similar change for IPv6 is provided in following patch.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c0725502

net/ipv4/ip_output.c

+12 −5
Original line number Diff line number Diff line
@@ -876,6 +876,7 @@ static int __ip_append_data(struct sock *sk, 
	unsigned int maxfraglen, fragheaderlen, maxnonfragsize;

	int csummode = CHECKSUM_NONE;

	struct rtable *rt = (struct rtable *)cork->dst;

	unsigned int wmem_alloc_delta = 0;

	u32 tskey = 0;



	skb = skb_peek_tail(queue);
@@ -971,10 +972,9 @@ static int __ip_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 + 15, 1,

					skb = alloc_skb(alloclen + hh_len + 15,

							sk->sk_allocation);

				if (unlikely(!skb))

					err = -ENOBUFS;
@@ -1033,6 +1033,11 @@ static int __ip_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;

		}
@@ -1079,12 +1084,13 @@ static int __ip_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:
@@ -1092,6 +1098,7 @@ static int __ip_append_data(struct sock *sk, 
error:

	cork->length -= length;

	IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTDISCARDS);

	refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);

	return err;

}