linux-kernel - Re: [PATCH, v9 3/3] cgroups: introduce timer slack controller

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Date:	Wed, 16 Mar 2011 04:35:45 -0700
From:	jacob pan <jacob.jun.pan@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Paul Menage <menage@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	containers@...ts.linux-foundation.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Matt Helsley <matthltc@...ibm.com>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH, v9 3/3] cgroups: introduce timer slack controller

On Mon, 14 Mar 2011 16:46:52 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 14 Mar 2011 16:05:24 +0200
> Kirill A. Shutemov" <kirill@...temov.name> wrote:
> 
> > +Overview
> > +--------
> > +
> > +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.
> 
> (quoting myself from last time)
> 
> Why do we need a cgroup for this as opposed to (say) inheritance over
> fork(), or a system-wide knob, or a per-process/threadgroup knob, or
> just leaving the existing code as-is?  Presumably you felt that a
> cgroup approach is better for manageability, but you didn't tell us
> about this and you didn't explore alternative ways of solving the
> problem-which-you-didn't-describe.
> 
> 
> 
> 
> I'm still having trouble seeing why we should merge this.  Who will
> use it, and for what reason and what benefits will they see?
> Quantified benefits, if possible!
> 
I am planning to use it for doing resource management for a mobile
device where we classify applications by groups based on priority and
trust level. Then at runtime, I plan to use timer slack as one of the
knobs to penalize/manage them at different degree to reduce power
consumption (via reduction of #wake-ups in this case).

Thanks,

Jacob
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