linux-kernel - Re: [BUGFIX][RESEND] Fix the starving writes bug in the anticipatory IO scheduler

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Date:	Mon, 16 Jun 2008 18:01:11 -0700 (PDT)
From:	Divyesh Shah <dpshah@...gle.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	Divyesh Shah <dpshah@...gle.com>, axboe@...nel.dk,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [BUGFIX][RESEND] Fix the starving writes bug in the anticipatory
 IO scheduler

On Mon, 16 Jun 2008, Nick Piggin wrote:

> Well, thanks for the report and test case. I'm a bit out of the
> loop when it comes to IO scheduling these days, however the fix
> seems good to me.
>
> Does google still use AS scheduling? This doesn't introduce any
> performance regressions that you can tell?

Yes we use AS scheduler. Benchmarking results on workloads have shown that 
AS does as good a job (and better in some cases) as CFQ. When there is 
a single thread reading/writing to disk, AS performs as well as CFQ. With 
multiple threads doing IO such that there are a lot of outstanding 
requests, CFQ performs worse than AS in terms of throughput.

-Divyesh.
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