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Date: Fri, 14 Oct 2011 15:43:48 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Paul Menage <menage@google.com>, Li Zefan <lizf@cn.fujitsu.com>,
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        Kay Sievers <kay.sievers@vrfy.org>, lennart@poettering.net,
        harald@redhat.com, david@fubar.dk, greg@kroah.com
Subject: Re: [PATCH, v10 3/3] cgroups: introduce timer slack controller
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On Tue, 11 Oct 2011 19:15:29 +0300
"Kirill A. Shutemov" <kirill@shutemov.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?