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

From: Jens Axboe
Date: Thu Apr 26 2007 - 11:50:42 EST

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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