linux-kernel - Re: Major network performance regression in 3.7

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Date:	Sat, 05 Jan 2013 23:35:24 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Willy Tarreau <w@....eu>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Major network performance regression in 3.7

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
only.

> 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,
 					break;
 			}
 			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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