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

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Message-ID: <12146282628495-twc@hexane.ssi.swin.edu.au>
Date:	Sat, 28 Jun 2008 21:22:27 +1000
From:	Tim Connors <tconnors@...ro.swin.edu.au>
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>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: Re: [RFC v1] Tunable sched_mc_power_savings=n

Andi Kleen <andi@...stfloor.org> said on Fri, 27 Jun 2008 00:38:53 +0200:
> Peter Zijlstra wrote:
> 
> >> And your workload manager could just nice processes. It should probably
> >> do that anyways to tell ondemand you don't need full frequency.
> > 
> > Except that I want my nice 19 distcc processes to utilize as much cpu as
> > possible, but just not bother any other stuff I might be doing...
> 
> They already won't do that if you run ondemand and cpufreq. It won't
> crank up the frequency for niced processes.

Shouldn't there be a powernice, just as there is an ionice and a nice?
Just as you don't always want CPU priority and IO priority to be
coupled, Peter has just demonstrated a very good case where you don't
want power and CPU choices to be coupled.  Whether the ondemand
governor of CPUFreq counts a process as wanting the CPU to run at a
higher speed, and these scheduler decisions should be controlled by
powernice.  By default, perhaps a high powernice should equal a high
nice equal to a high ionice, but the user should be able to change
this.  The last thing you want is a distcc process taking up lots of
time, burning more Joules because it runs 10 times longer with only
half the power.  It's not a nice choice between that and running at
nice 0 where it interferes with the user's editing.
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