| From | Greg Kroah-Hartman <> | Subject | [ 56/61] tcp: dont abort splice() after small transfers | Date | Tue, 12 Feb 2013 12:35:16 -0800 |
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3.7-stable review patch. If anyone has any objections, please let me know.
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From: Willy Tarreau <w@1wt.eu>
[ Upstream commit 02275a2ee7c0ea475b6f4a6428f5df592bc9d30b ]
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- net/ipv4/tcp.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
--- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1490,15 +1490,19 @@ int tcp_read_sock(struct sock *sk, read_ 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);
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