netdev - Re: Data corruption issue with splice() on 2.6.27.10

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Message-ID: <20090106155715.GA28783@1wt.eu>
Date:	Tue, 6 Jan 2009 16:57:15 +0100
From:	Willy Tarreau <w@....eu>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: Data corruption issue with splice() on 2.6.27.10

On Tue, Jan 06, 2009 at 10:01:13AM +0000, Jarek Poplawski wrote:
> On Tue, Jan 06, 2009 at 10:41:38AM +0100, Willy Tarreau wrote:
> ...
> > > Great story! Alas I don't understand this fully either, but it seems
> > > Changli Gao was concerned with sendpage sending this "as pages", so
> > > when NETIF_F_SG flag is available. Did you try this without SG btw?
> > 
> > No I did not. I can try, it's not too hard. It would in part defeat the
> > purpose of the mechanism (especially at 10 Gbps) but at least it will
> > help narrow the problem down.
> 
> Yes, I meant it only as a proof of concept. BTW, delaying TCP acks a
> bit for these sendpages should then make it more reproducible, I guess.

OK here is an update. It does not change anything to turn off any acceleration
feature on the interface (tg3) :

root@...p:~# ethtool -k eth0
Offload parameters for eth0:
rx-checksumming: off
tx-checksumming: off
scatter-gather: off
tcp segmentation offload: off

It still forwards corrupted data like mad. I noticed that the corruption rate
is 10-100 times higher when forwarding from eth0 to eth0 than from eth0 to lo.

Maybe this can help find the culprit ?

Willy

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