linux-kernel - Re: [PATCH, v10 3/3] cgroups: introduce timer slack controller

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Message-Id: <20111014154348.ae6267aa.akpm@linux-foundation.org>
Date:	Fri, 14 Oct 2011 15:43:48 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Paul Menage <menage@...gle.com>, Li Zefan <lizf@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	containers@...ts.linux-foundation.org,
	jacob.jun.pan@...ux.intel.com,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Matt Helsley <matthltc@...ibm.com>,
	linux-api@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	lennart@...ttering.net, harald@...hat.com, david@...ar.dk,
	greg@...ah.com
Subject: Re: [PATCH, v10 3/3] cgroups: introduce timer slack controller

On Tue, 11 Oct 2011 19:15:29 +0300
"Kirill A. Shutemov" <kirill@...temov.name> wrote:

> Every task_struct has timer_slack_ns value. This value uses to round up
> poll() and select() timeout values. This feature can be useful in
> mobile environment where combined wakeups are desired.
> 
> Originally, prctl() was the only way to change timer slack value of
> a process. So you was not able change timer slack value of another
> process.
> 
> cgroup subsys "timer_slack" implements timer slack controller. It
> provides a way to set minimal timer slack value for a group of tasks.
> If a task belongs to a cgroup with minimal timer slack value higher than
> task's value, cgroup's value will be applied.
> 
> Timer slack controller allows to implement setting timer slack value of
> a process based on a policy. For example, you can create foreground and
> background cgroups and move tasks between them based on system state.

I'm having trouble understanding the value of this feature.  Users can
presently control the timer-slack of a group of processes via
inherit-over-fork.

Perhaps there's a case for providing a way for process A to set process
B's slack.  And perhaps B's children.  That would be a simpler patch
and would have the considerable advantage that it doesn't require
cgroups.

So.... why should we merge this?
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