linux-kernel - Re: [RFC v1] Tunable sched_mc_power

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Message-ID: <20080628125349.GB22099@srcf.ucam.org>
Date:	Sat, 28 Jun 2008 13:53:49 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, dipankar@...ibm.com,
	balbir@...ux.vnet.ibm.com,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: Re: [RFC v1] Tunable sched_mc_power_savings=n

On Sat, Jun 28, 2008 at 02:36:02PM +0200, Andi Kleen wrote:

> For example if you're in a data center at a specific operating point and
> you would need to crank up the air condition at significant power cost it might
> be well better overall to force all servers to a lower operating point
> and avoid that.

Sure, there are cases where you have additional constraints. But within 
those constraints, you probably want to run as fast as possible.

> That said in general you all should have complained when ondemand behaviour
> was introduced.

ignore_nice seems to be set to 0 by default?

> Also it's unclear that the general "race to idle" heuristic really
> applies to the case of the "keep sockets idle" power optimization
> that started this thread.
> 
> Usually package C states bring much more than core C states
> and keeping another package completely idle saves likely
> more power than the power cost of running something a little
> bit slower on a package that is already busy on another core.

I'd agree with that.
-- 
Matthew Garrett | mjg59@...f.ucam.org
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