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

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Date:	Thu, 8 Jan 2009 18:14:19 +0100
From:	Willy Tarreau <w@....eu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jarek Poplawski <jarkao2@...il.com>, Ben Mansell <ben@...s.com>,
	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 Thu, Jan 08, 2009 at 03:53:00PM +0100, Ingo Molnar wrote:
> 
> * Willy Tarreau <w@....eu> wrote:
> 
> > On Thu, Jan 08, 2009 at 07:16:51AM +0000, Jarek Poplawski wrote:
> > > On 06-01-2009 19:15, Willy Tarreau wrote:
> > > ...
> > > > Ah, so you might also have discovered a few annoyances with the API, eg
> > > > the fact that splice() returns after the first read in non-blocking mode,
> > > > as well as the fact that it never returns zero on close, but -EAGAIN,
> > > > which requires an additional recv(MSG_PEEK) to distinguish between a
> > > > close and a lack of data. But I leave that for a later discussion, let's
> > > > address the corruption issue first.
> > > 
> > > FYI, this should be just fixed:
> > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=4f7d54f59bc470f0aaa932f747a95232d7ebf8b1
> > > 
> > 
> > Ah cool, thanks Jarek for notifying us. Indeed, it's the exact same patch
> > I had pending here ;-)
> > 
> > I'll ping Greg for a backport into -stable, as applications relying on 
> > this will clearly not work without that fix.
> > 
> > The other one I had consists in removing "|| !timeo" at the end of the 
> > loop, because otherwise splice() returns very small chunks (typically 
> > 1448 or 1460 bytes), leading to disastrous performance on high bandwidth 
> > links. At 10 Gbps, this means about 800000 calls to splice() per second!
> 
> looks interesting - would you mind to submit it?

OK I will. I preferred to focus on the bug first, which is clearly
more annoying since it basically makes splice() unusuable in a proxy.
I wanted to avoid changes before the bug is fixed, but now, with the
first investigations, it seems that the fix will be in a different
area anyway so that doesn't matter.

Regards,
Willy

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