linux-kernel - Re: [PATCH 11/23] io-controller: Introduce group idling

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Message-ID: <4A99C9FC.2010004@redhat.com>
Date:	Sat, 29 Aug 2009 20:38:20 -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,
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	akpm@...ux-foundation.org, peterz@...radead.org,
	jmarchan@...hat.com, torvalds@...ux-foundation.org, mingo@...e.hu
Subject: Re: [PATCH 11/23] io-controller: Introduce group idling

Vivek Goyal wrote:
> o It is not always that IO from a process or group is continuous. There are
>   cases of dependent reads where next read is not issued till previous read
>   has finished. For such cases, CFQ introduced the notion of slice_idle,
>   where we idle on the queue for sometime hoping next request will come
>   and that's how fairness is provided otherwise queue will be deleted
>   immediately from the service tree and this process will not get the
>   fair share.
> 
> o This patch introduces the similar concept at group level. Idle on the group
>   for a period of "group_idle" which is tunable through sysfs interface. So
>   if a group is empty and about to be deleted, we idle for the next request.
> 
> o This patch also introduces the notion of wait busy where we wait for one
>   extra group_idle period even if queue has consumed its time slice. The
>   reason being that group will loose its share upon removal from service
>   tree as some other entity will be picked for dispatch and vtime jump will
>   take place.
> 
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>

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

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