linux-kernel - Re: [PATCH 5/15] cfq-iosched: speed up rbtree handling

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Message-ID: <20070426154643.GB2017@kernel.dk>
Date:	Thu, 26 Apr 2007 17:46:44 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Alan.Brunelle@...ox.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/15] cfq-iosched: speed up rbtree handling

On Thu, Apr 26 2007, Alan D. Brunelle wrote:
> Jens Axboe wrote:
> >On Wed, Apr 25 2007, Jens Axboe wrote:
> >>On Wed, Apr 25 2007, Jens Axboe wrote:
> >>>On Wed, Apr 25 2007, Alan D. Brunelle wrote:
> >>>>Hi Jens -
> >>>>
> >>>>The attached patch speeds it up even more - I'm finding a >9% reduction 
> >>>>in %system with no loss in IO performance. This just sets the cached 
> >>>>element when the first is looked for.
> >>>Interesting, good thinking. It should not change the IO pattern, as the
> >>>end result should be the same. Thanks Alan, will commit!
> >>>
> >>>I'll give elevator.c the same treatment, should be even more beneficial.
> >>>Stay tuned for a test patch.
> >>Something like this, totally untested (it compiles). I initially wanted
> >>to fold the cfq addon into the elevator.h provided implementation, but
> >>that requires more extensive changes. Given how little code it is, I
> >>think I'll keep them seperate.
> >
> >Booted, seems to work fine for me. In a null ended IO test, I get about
> >a 1-2% speedup for a single queue of depth 64 using libaio. So it's
> >definitely worth it, will commit.
> >
> After longer runs last night, I think the patched elevator code /does/ 
> help (albeit ever so slightly - about 0.6% performance improvement at a 
> 1.1% %system overhead).
> 
>  rkB_s    %system  Kernel
> ---------  -------  ----------------------------------------------------
> 1022942.2     3.69  Original patch + fix to cfq_rb_first
> 1029087.0     3.73  This patch stream (including fixes to elevator code)

Ah good, thanks for testing! It's all in the cfq branch now.

-- 
Jens Axboe

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