linux-kernel - Re: Cfq first request patch changes IO performance

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Date:	Tue, 27 Feb 2007 21:39:54 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Ananiev, Leonid I" <leonid.i.ananiev@...el.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Cfq  first request patch changes IO performance

On Mon, Feb 26 2007, Ananiev, Leonid I wrote:
> The patch "cfq-iosched: defer slice activation to first request being
> active"
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=c
> ommitdiff;h=44f7c16065c83060cbb9dd9b367141682a6e2b8e;hp=99f9628aba4d8fb3
> b8d955c9efded0d0a1995fad
> 
> Sysbench fileio (random read/write mix)	-15%
> Tiobench sequential write		-3%
> Tiobench random write 			-5%
> Iozone record re-write			-21%
> Iozone mmap sequential read 		-20%
> Iozone mmap random write		+45%
> Aio-stress direct sequential read		+29%
> For other 3 tiobench, 7 aiostress and 13 iozone tests the result changes
> are less than variation.
> 
> Considered patch does not impact on performance if all threads have
> equal IO activity (tiobench).
> If single thread has IO activity the performance becomes unstable and is
> decreased mainly.

Yep there are a few unfortunate side effects, I have later fixed those.
I just need to split that patchset up and commit it.

-- 
Jens Axboe

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