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tcp: don't abort splice() after small transfers 

TCP coalescing added a regression in splice(socket->pipe) performance,
for some workloads because of the way tcp_read_sock() is implemented.

The reason for this is the break when (offset + 1 != skb->len).

As we released the socket lock, this condition is possible if TCP stack
added a fragment to the skb, which can happen with TCP coalescing.

So let's go back to the beginning of the loop when this happens,
to give a chance to splice more frags per system call.

Doing so fixes the issue and makes GRO 10% faster than LRO
on CPU-bound splice() workloads instead of the opposite.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willy Tarreau 2012-12-02 11:49:27 +00:00 committed by David S. Miller
parent 077b393d05
commit 02275a2ee7
1 changed files with 8 additions and 4 deletions
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12
net/ipv4/tcp.c
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@ -1494,15 +1494,19 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
copied += used;
offset += used;
}
/*
* If recv_actor drops the lock (e.g. TCP splice
/* If recv_actor drops the lock (e.g. TCP splice
* receive) the skb pointer might be invalid when
* getting here: tcp_collapse might have deleted it
* while aggregating skbs from the socket queue.
*/
skb = tcp_recv_skb(sk, seq-1, &offset);
if (!skb || (offset+1 != skb->len))
skb = tcp_recv_skb(sk, seq - 1, &offset);
if (!skb)
break;
/* TCP coalescing might have appended data to the skb.
* Try to splice more frags
*/
if (offset + 1 != skb->len)
continue;
}
if (tcp_hdr(skb)->fin) {
sk_eat_skb(sk, skb, false);