linux-kernel - Re: [patch]cfq-iosched: delete deep seeky queue idle logic

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Date:	Fri, 16 Sep 2011 22:50:17 +0800
From:	Tao Ma <tm@....ma>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Jens Axboe <jaxboe@...ionio.com>,
	Maxim Patlasov <maxim.patlasov@...il.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Corrado Zoccolo <czoccolo@...il.com>
Subject: Re: [patch]cfq-iosched: delete deep seeky queue idle logic

On 09/16/2011 10:08 PM, Christoph Hellwig wrote:
> On Fri, Sep 16, 2011 at 05:54:51PM +0800, Tao Ma wrote:
>> This year's FAST has a paper named "A Scheduling Framework That Makes
>> Any Disk Schedulers Non-Work-Conserving Solely Based on Request
>> Characteristics". It has described this situation and suggests a new
>> scheduler named "stream scheduler" to resolve this. But I am not sure
>> whether CFQ can work like that or not.
> 
> As usual I suspect the best thing is to just use noop for these kinds of
> cases.  E.g. when you use xfs with the filestreams options you'll get
> patterns pretty similar to that in the initial post  - that is
> intentional as it is generally use to place them into different areas
> of a complex RAID array.  Any scheduler "smarts" will just help to break these
> I/O streams.
yeah, actually the paper does show that the performance of cfq is worse
than noop in this case. ;) See section 3.4 if you are interested.

Thanks
Tao
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