linux-kernel - Re: [RFC PATCH v1 0/3] Saving power by cpu evacuation using sched

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Date:	Mon, 27 Apr 2009 05:52:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arjan van de Ven <arjan@...radead.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arun Bharadwaj <arun@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH v1 0/3] Saving power by cpu evacuation using
	sched_mc=n


* Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:

> Test results for ebizzy 8 threads at various sched_mc settings has 
> been summarised with relative values below. The test platform is 
> dual socket quad core x86 system (pre-Nehalem).
> 
> --------------------------------------------------------
> sched_mc	No Cores	Performance	AvgPower	
> 		used		Records/sec	(Watts)
> --------------------------------------------------------
> 0		8		1.00x		1.00y
> 1		8		1.02x		1.01y
> 2		8		0.83x		1.01y
> 3		7		0.86x		0.97y
> 4		6		0.76x		0.92y
> 5		4		0.72x		0.82y
> --------------------------------------------------------

Looks like we want the kernel default to be sched_mc=1 ?

Regarding the values for 2...5 - is the AvgPower column time 
normalized or workload normalized?

If it's time normalized then it appears there's no power win here at 
all: we'd be better off by throttling the workload directly (by 
injecting sleeps or something like that), right?

	Ingo
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