linux-kernel - Re: Analysis of sched_mc_power

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Message-ID: <20080109132014.GF27196@elte.hu>
Date:	Wed, 9 Jan 2008 14:20:14 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	discuss@...sWatts.org,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	venkatesh.pallipadi@...el.com, tglx@...utronix.de,
	Arjan van de Ven <arjan@...radead.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	Chanda Sethia <chanda.sethia@...ibm.com>
Subject: Re: Analysis of sched_mc_power_savings

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

> I will watch this during the experiments.  I have been using klog 
> application to dump relayfs data.  I did run powertop and top as well, 
> I will bind them to certain CPUs and isolate their impact.
> 
> I believe the margin of error would be less since all the measurement 
> tasks sleep for long duration.

ok, long duration ought to be enough.

i think a possible explanation of your observtions would be this: sleepy 
workloads are affected more by the wakeup logic, and most of the 
power-savings works via runtime balancing.

So perhaps try to add some SD_POWERSAVINGS_BALANCE logic to 
try_to_wake_up()? I think waking up on the same CPU where it went to 
sleep is the most power-efficient approach in general. (or always waking 
up where the wakee runs - this should be measured.) Right now 
try_to_wake_up() tries to spread out load opportunistically, which is 
throughput-maximizing but it's arguably not very power conscious.

	Ingo
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