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SubjectRe: [PATCH, v9 3/3] cgroups: introduce timer slack controller
On Mon, 14 Mar 2011 16:46:52 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon, 14 Mar 2011 16:05:24 +0200
> Kirill A. Shutemov" <kirill@shutemov.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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