linux-kernel - Re: [PATCH 17/23] io-controller: anticipatory changes for hierarchical fair queuing

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Message-ID: <4A9C068C.2020008@redhat.com>
Date:	Mon, 31 Aug 2009 13:21:16 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com,
	taka@...inux.co.jp, guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	righi.andrea@...il.com, m-ikeda@...jp.nec.com, agk@...hat.com,
	akpm@...ux-foundation.org, peterz@...radead.org,
	jmarchan@...hat.com, torvalds@...ux-foundation.org, mingo@...e.hu
Subject: Re: [PATCH 17/23] io-controller: anticipatory changes for hierarchical
 fair queuing

Vivek Goyal wrote:
> This patch changes anticipatory scheduler to use queue scheduling code from
> elevator layer.  One can go back to old as by deselecting
> CONFIG_IOSCHED_AS_HIER. Even with CONFIG_IOSCHED_AS_HIER=y, with-out any
> other cgroup created, AS behavior should remain the same as old.
> 
> o AS is a single queue ioschduler, that means there is one AS queue per group.
> 
> o common layer code select the queue to dispatch from based on fairness, and
>   then AS code selects the request with-in group.
> 
> o AS runs reads and writes batches with-in group. So common layer runs timed
>   group queues and with-in group time, AS runs timed batches of reads and
>   writes.
> 
> o Note: Previously AS write batch length was adjusted synamically whenever
>   a W->R batch data direction took place and when first request from the
>   read batch completed.
> 
>   Now write batch updation takes place when last request from the write
>   batch has finished during W->R transition.
> 
> o AS runs its own anticipation logic to anticipate on reads. common layer also
>   does the anticipation on the group if think time of the group is with-in
>   slice_idle.
> 
> o Introduced few debugging messages in AS.
> 
> Signed-off-by: Nauman Rafique <nauman@...gle.com>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>

Acked-by: Rik van Riel <riel@...hat.com>

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