Re: Major network performance regression in 3.7

From: Eric Dumazet
Date: Sun Jan 06 2013 - 02:35:17 EST

On Sun, 2013-01-06 at 03:52 +0100, Willy Tarreau wrote:

> OK so I observed no change with this patch, either on the loopback
> data rate at >16kB MTU, or on the myri. I'm keeping it at hand for
> experimentation anyway.

Yeah, there was no bug. I rewrote it for net-next as a cleanup/optim

> Concerning the loopback MTU, I find it strange that the MTU changes
> the splice() behaviour and not send/recv. I thought that there could
> be a relation between the MTU and the pipe size, but it does not
> appear to be the case either, as I tried various sizes between 16kB
> and 256kB without achieving original performance.

It probably is related to a too small receive window, given the MTU was
multiplied by 4, I guess we need to make some adjustments

You also could try :

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 1ca2536..b68cdfb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1482,6 +1482,9 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
used = recv_actor(desc, skb, offset, len);
+ /* Clean up data we have read: This will do ACK frames. */
+ if (used > 0)
+ tcp_cleanup_rbuf(sk, used);
if (used < 0) {
if (!copied)
copied = used;

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