linux-kernel - Re: [PATCH, v8 1/3] hrtimer: introduce effective timer slack

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Date:	Thu, 3 Mar 2011 17:32:28 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	"Kirill A. Shutsemov" <kirill@...temov.name>
Cc:	Paul Menage <menage@...gle.com>, Li Zefan <lizf@...fujitsu.com>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-api@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH, v8 1/3] hrtimer: introduce effective timer slack

On Thursday 03 March 2011, Kirill A. Shutsemov wrote:
> task_get_effective_timer_slack() returns timer slack value to be used
> to configure per-task timers. It can be equal or higher than task's
> timer slack value.
> 
> For now task_get_effective_timer_slack() returns timer_slack_ns of the
> task. Timer slack cgroup controller will implement a bit more
> sophisticated logic.

Some time ago, there was a discussion about a method for automatically
determining timer slack values, and I think nobody ever implemented it.

The idea was to penalize tasks that have timers expiring a lot, typically
a sign of programs that were not written with power consumption in mind.

I think that could be nicely combined with your patch. Instead of setting
the effective timer slack for the entire control group, you  could
set a target value that is applied only to tasks that have their timers
expire frequently. When a timer expires for a task, you increase the
effective slack up to the maximum, and when you set up a timer, you
decrease it again. The amount by which the effective slack gets changed
can depend on how long ago the last timer expired.

Does this make sense to you?

	Arnd
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