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

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Message-ID: <4863AF57.3040005@linux.vnet.ibm.com>
Date:	Thu, 26 Jun 2008 20:31:43 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	svaidy@...ux.vnet.ibm.com,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: Re: [RFC v1] Tunable sched_mc_power_savings=n

Andi Kleen wrote:
> Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> writes:
>> The idea being proposed is to enhance the tunable with varied degrees
>> of consolidation that can work best for different workload
>> characteristics.  echo 2 > /sys/.../sched_mc_power_savings could
>> enable more aggressive consolidation than the default.
> 
> It would be better to fix the single power saving default to work
> better with bursty workloads too than to add more tunables. Tunables
> are basically "we give up, let's push the problem to the user"
> which is not nice. I suspect a lot of users won't even know if their
> workloads are bursty or not.  Or they might have workloads which
> are both bursty and not bursty.
> 
> Or did you try that and failed?
> 

A user could be an application and certain applications can predict their
workload. For example, a database, a file indexer, etc can predict their workload.

Policies are best known in user land and the best controlled from there.
Consider a case where the end user might select a performance based policy or a
policy to aggressively save power (during peak tariff times). With
virtualization, the whole concept of application is changing, the OS by itself
could be an application :)


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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