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

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Date:	Mon, 30 Jun 2008 16:31:40 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	davecb@....com
CC:	svaidy@...ux.vnet.ibm.com,
	Tim Connors <tconnors@...ro.swin.edu.au>,
	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

David Collier-Brown wrote:
> Vaidyanathan Srinivasan wrote:
>> I am trying to find answer to the question: Should we have the power
>> saving tunable as 'nice' value per process or system wide?
>>
>> How should we interpret the POWER parameter in a datacenter with power
>> constraint as mentioned in this thread?  Or in a simple case of AC vs
>> battery in a laptop.
> 
> I agree with Tim re setting them all independently, 

I agree that powernice is likely a good idea (although the semantics
are not 100% clear yet), but there's still the issue
(shared with ionice) that 99.99+% of all setups won't set powernice
explicitely  so you still need a reasonable default when it is not
set.

Me thinks the correct strategy would be something like this:

- When powernice is set prefer it
- For the idle socket optimization: use nice because it's
unclear that "race to idle" applies here.
- For ondemand: when nice is set behave more like the conservative
governor and take longer to crank up [this might be controversal]

Also are the best powernice semantics the same between idle
sockets and ondemand? I'm not sure.


and suggest that
> they're all really per-process values: setting power saving system-wide
> is meaningful, but so are individual settings.
> There is therefor an argument for making them subsets of
> a higher-level nice program.
> 
> Mind you, the order in which one *implements* the capability,
> and whether one does powernice first and adds it to nice later
> is your call!  I have no idea of how hard what I suggested is (;-))

In general for Linux deployment it tends to be easier
to provide another package with an own command instead of
patching a core package like coreutils

With an own package you can just tell the user
"type (yum|zypper|apt-get|...) install powernice",
while an updated coreutils tends to be more trouble or even
require a distribution update.

-Andi


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