linux-kernel - Re: Slow file transfer speeds with CFQ IO scheduler in some cases

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Date:	Mon, 10 Nov 2008 18:35:04 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Vitaly V. Bursov" <vitalyb@...enet.dn.ua>
Cc:	Jeff Moyer <jmoyer@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Slow file transfer speeds with CFQ IO scheduler in some cases

On Mon, Nov 10 2008, Vitaly V. Bursov wrote:
> Jens Axboe wrote:
> > On Mon, Nov 10 2008, Jeff Moyer wrote:
> >> Jens Axboe <jens.axboe@...cle.com> writes:
> >>
> >>> http://bugzilla.kernel.org/attachment.cgi?id=18473&action=view
> >> Funny, I was going to ask the same question.  ;)  The reason Jens wants
> >> you to try this patch is that nfsd may be farming off the I/O requests
> >> to different threads which are then performing interleaved I/O.  The
> >> above patch tries to detect this and allow cooperating processes to get
> >> disk time instead of waiting for the idle timeout.
> > 
> > Precisely :-)
> > 
> > The only reason I haven't merged it yet is because of worry of extra
> > cost, but I'll throw some SSD love at it and see how it turns out.
> > 
> 
> Sorry, but I get "oops" same moment nfs read transfer starts.
> I can get directory list via nfs, read files locally (not
> carefully tested, though)
> 
> Dumps captured via netconsole, so these may not be completely accurate
> but hopefully will give a hint.

Interesting, strange how that hasn't triggered here. Or perhaps the
version that Jeff posted isn't the one I tried. Anyway, search for:

        RB_CLEAR_NODE(&cfqq->rb_node);

and add a

        RB_CLEAR_NODE(&cfqq->prio_node);

just below that. It's in cfq_find_alloc_queue(). I think that should fix
it.

-- 
Jens Axboe

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