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

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Message-Id: <20110314164652.5b44fb9e.akpm@linux-foundation.org>
Date:	Mon, 14 Mar 2011 16:46:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Paul Menage <menage@...gle.com>, Li Zefan <lizf@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	containers@...ts.linux-foundation.org,
	jacob.jun.pan@...ux.intel.com,
	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 16:05:24 +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!

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