linux-kernel - Re: [PATCH 20/23] io-controller: Per cgroup request descriptor support

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Date:	Mon, 31 Aug 2009 13:54:44 -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 20/23] io-controller: Per cgroup request descriptor support

Vivek Goyal wrote:
> o Currently a request queue has got fixed number of request descriptors for
>   sync and async requests. Once the request descriptors are consumed, new
>   processes are put to sleep and they effectively become serialized. Because
>   sync and async queues are separate, async requests don't impact sync ones
>   but if one is looking for fairness between async requests, that is not
>   achievable if request queue descriptors become bottleneck.
> 
> o Make request descriptor's per io group so that if there is lots of IO
>   going on in one cgroup, it does not impact the IO of other group.
> 
> o This patch implements the per cgroup request descriptors. request pool per
>   queue is still common but every group will have its own wait list and its
>   own count of request descriptors allocated to that group for sync and async
>   queues. So effectively request_list becomes per io group property and not a
>   global request queue feature.
> 
> o Currently one can define q->nr_requests to limit request descriptors
>   allocated for the queue. Now there is another tunable q->nr_group_requests
>   which controls the requests descriptr limit per group. q->nr_requests
>   supercedes q->nr_group_requests to make sure if there are lots of groups
>   present, we don't end up allocating too many request descriptors on the
>   queue.
> 
> 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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