linux-kernel - Re: [PATCH 14/16] blkio: Idle on a group for some time on rotational media

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Date:	Fri, 13 Nov 2009 11:58:53 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com,
	taka@...inux.co.jp, guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	m-ikeda@...jp.nec.com, akpm@...ux-foundation.org, riel@...hat.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 14/16] blkio: Idle on a group for some time on rotational 
	media

Hi Vivek,
On Fri, Nov 13, 2009 at 12:32 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> o If a group is not continuously backlogged, then it will be deleted from
>  service tree and loose it share. For example, if a single random seeky
>  reader or a single sequential reader is running in group.
>
Without groups, a single sequential reader would already have its 10ms
idle slice, and a single random reader on the noidle service tree
would have its 2ms idle, before switching to a new workload. Were
those removed in the previous patches (and this patches re-enable
them), or this introduces an additional idle between groups?

> o One solution is to let group loose it share if it is not backlogged and
>  other solution is to wait a bit for the slow group so that it can get its
>  time slice. This patch implements waiting for a group to wait a bit.
>
> o This waiting is disabled for NCQ SSDs.
>
> o This patch also intorduces the tunable "group_idle" which can enable/disable
>  group idling manually.
>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>

Thanks,
Corrado
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