linux-kernel - Re: [PATCH 1/2] cfq: always return false from should_idle if slice

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Message-ID: <4C1FC4CA.7030007@kernel.dk>
Date:	Mon, 21 Jun 2010 22:00:10 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Jeff Moyer <jmoyer@...hat.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] cfq: always return false from should_idle if slice_idle
 is set to zero

On 21/06/10 21.49, Jeff Moyer wrote:
> Hi,
> 
> In testing a competing fsync-ing process and a sequential reader on
> mid-grade storage, I found that cfq was incapable of achieving the I/O
> rates of deadline, no matter how it was tuned.  Investigation, and insight
> from Vivek (mostly the latter), led to identifying that we were still
> idling for the last queue in the service tree.
> 
> Modifying cfq_should_idle to not idle when slice_idle is set to zero got
> us much closer to the performance of deadline for this workload.  I have
> one follow-on patch that gets us on-par with deadline, but I think this
> patch stands alone.
> 
> Comments, as always, are appreciated.

This looks good.

-- 
Jens Axboe

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