From 02275a2ee7c0ea475b6f4a6428f5df592bc9d30b Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Sun, 2 Dec 2012 11:49:27 +0000 Subject: [PATCH] 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 Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 1aca02c9911e..8fc5b3bd6075 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -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); -- 2.30.2