linux-kernel - Re: [patch v5 10/15] sched: packing transitory tasks in wake/exec power balancing

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Date:	Wed, 20 Feb 2013 16:11:45 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Mike Galbraith <efault@....de>, peterz@...radead.org
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	torvalds@...ux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
	morten.rasmussen@....com
Subject: Re: [patch v5 10/15] sched: packing transitory tasks in wake/exec
 power balancing

On 02/20/2013 03:40 PM, Mike Galbraith wrote:
> On Wed, 2013-02-20 at 13:55 +0800, Alex Shi wrote:
> 
>> Joonsoo Kim suggests not packing exec task, since the old task utils is
>> possibly unuseable.
> 
> (I'm stumbling around in rtmutex PI land, all dazed and confused, so
> forgive me if my peripheral following of this thread is off target;)
> 
> Hm, possibly.  Future behavior is always undefined, trying to predict
> always a gamble... so it looks to me like not packing on exec places a
> bet against the user, who chose to wager that powersaving will happen
> and it won't cost him too much, if you don't always try to pack despite
> any risks.  The user placed a bet on powersaving, not burst performance.
> 
> Same for the fork, if you spread to accommodate a potential burst, you
> bin the power wager, so maybe it's not in his best interest.. fork/exec
> is common, if it's happening frequently, you'll bin the potential power
> win frequently, reducing effectiveness, and silently trading power for
> performance when the user asked to trade performance for a lower
> electric bill.
> 
> Dunno, just a thought, but I'd say for powersaving policy, you have to
> go just for broke and hope it works out.  You can't know it won't, but
> you'll toss potential winnings every time you don't roll the dice.


Sounds reasonable too.

I have no idea of the of the decision now.
And guess many guys dislike to use a knob to let user do the choice.

What's your opinions, Peter?
> 
> -Mike
> 


-- 
Thanks Alex
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