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

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Message-ID: <20090107125535.GC6307@1wt.eu>
Date:	Wed, 7 Jan 2009 13:55:35 +0100
From:	Willy Tarreau <w@....eu>
To:	Evgeniy Polyakov <zbr@...emap.net>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	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 Wed, Jan 07, 2009 at 03:46:29PM +0300, Evgeniy Polyakov wrote:
> On Wed, Jan 07, 2009 at 11:42:46PM +1100, Herbert Xu (herbert@...dor.apana.org.au) wrote:
> > > Doesn't your tcp fallbacks to kernel_sendmsg() without sg in
> > > tcp_sendpage()? And then just feeds data into the stack the same way it
> > > happens with send() i.e. by copying it.
> > 
> > Good point.  Did he check GSO though? GSO will always enable SG
> > on the socket regardless of the netdev's setting.  And if the device
> > started out with SG enabled then recent kernels will enable GSO
> > by default.
> 
> Willy, what was the kernel you are tested no-accel behaviour and what
> were the gso settings?

kernel is 2.6.27.10 + a few patches (squashfs, etc..., nothing related to
this area). My ethtool is a bit old and does not report GSO. I'll download
and rebuild a more recent one and retest.

> Can you add a simple single print into tcp_sendpage() to determine if
> content was copied or fed into do_tcp_sendpages() otherwise?

Yes, will do that too.

Willy

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