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

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Date:	Thu, 26 Apr 2007 10:28:29 -0400
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	linux-kernel@...r.kernel.org
Cc:	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 5/15] cfq-iosched: speed up rbtree handling

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)

Alan



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