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

On Mon, 14 Mar 2011 16:46:52 -0700
Andrew Morton [off-list ref] wrote:

On Mon, 14 Mar 2011 16:05:24 +0200
Kirill A. Shutemov" [off-list ref] wrote:

quoted

+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