This is a note to let you know that I've just added the patch titled
tcp: don't abort splice() after small transfers
to the 3.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-don-t-abort-splice-after-small-transfers.patch
and it can be found in the queue-3.7 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From a037491fdc5e5ca2b6f21366b1165555e285c71d Mon Sep 17 00:00:00 2001
From: Willy Tarreau <[email protected]>
Date: Sun, 2 Dec 2012 11:49:27 +0000
Subject: tcp: don't abort splice() after small transfers
From: Willy Tarreau <[email protected]>
[ 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 <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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);
Patches currently in stable-queue which might be from [email protected] are
queue-3.7/net-splice-avoid-high-order-page-splitting.patch
queue-3.7/tcp-fix-splice-and-tcp-collapsing-interaction.patch
queue-3.7/tcp-don-t-abort-splice-after-small-transfers.patch
queue-3.7/net-splice-fix-__splice_segment.patch
queue-3.7/tcp-splice-fix-an-infinite-loop-in-tcp_read_sock.patch
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