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

[jacob pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Mon, 14 Mar 2011 16:46:52 -0700
Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> wrote:

> On Mon, 14 Mar 2011 16:05:24 +0200
> Kirill A. Shutemov" <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org> 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