linux-kernel - Re: [PATCH V3 0/22] sched: simplified fork, enable load average into LB and power awareness scheduling

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Message-ID: <50EE3A66.4060407@intel.com>
Date:	Thu, 10 Jan 2013 11:49:58 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Morten Rasmussen <Morten.Rasmussen@....com>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"bp@...en8.de" <bp@...en8.de>, "pjt@...gle.com" <pjt@...gle.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"efault@....de" <efault@....de>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 0/22] sched: simplified fork, enable load average into
 LB and power awareness scheduling

>>
>> 3, power awareness scheduling, patch 13~22,
>> The subset implement my previous power aware scheduling proposal:
>> https://lkml.org/lkml/2012/8/13/139
>> It defines 2 new power aware policy balance and powersaving, and then
>> try to spread or pack tasks on each of sched group level according the
>> different scheduler policy. That can save much power when task number in
>> system is no more then LCPU number.
> 
> Interesting stuff. I have read through your patches, but it is still not
> clear to me what metrics you use to determine whether a sched group is
> fully utilized or if it can be used for packing more tasks. Is it based on
> nr_running or PJT's tracked load or both? How is the threshold defined?

Thanks review, Morten!

cpu utilisation = rq->util * (rq->nr_running? rq->running : 1),
here: rq->util = running time / whole period.

If nr_running == 2, util == 99%, the potential max 'utilisation' is 99 *
2 = 198, because both of tasks may has the possibility to run full time.

group utils = Sum of all cpu's util,
like a 2 LCPU group, A nr_running is 0, B cpu util is 99%, and has 3 tasks,
So, the group utils = A'util + 99 * 3, that is bigger than threshold =
99% * 2.

The above calculation bias to performance, and that is our purpose.

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