3.6.11.1 stable review patch.
If anyone has any objections, please let me know.
------------------
From: Willy Tarreau <w@xxxxxx>
[ Upstream commit e9feca83d1496afabd0cc174863646e6d7101d85 ]
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@xxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
---
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 b0b39f6..5fe7a59 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1517,15 +1517,19 @@ 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);
--
1.7.10.4
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