linux-kernel - Re: [discussion]sched: a rough proposal to enable power saving in scheduler

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Date:	Thu, 16 Aug 2012 12:57:43 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	vincent.guittot@...aro.org, svaidy@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in
 scheduler

On 08/15/2012 10:24 PM, Rakib Mullick wrote:

> On 8/13/12, Alex Shi <alex.shi@...el.com> wrote:
>> Since there is no power saving consideration in scheduler CFS, I has a
>> very rough idea for enabling a new power saving schema in CFS.
>>
>> It bases on the following assumption:
>> 1, If there are many task crowd in system, just let few domain cpus
>> running and let other cpus idle can not save power. Let all cpu take the
>> load, finish tasks early, and then get into idle. will save more power
>> and have better user experience.
>>
> This assumption indirectly point towards the scheme when performance
> is enabled, isn't it? Cause you're trying to spread the load equally
> amongst all the CPUs.


It is.

> 
>>
>> select_task_rq_fair()
>> {

	int powersaving = 0;

>> 	for_each_domain(cpu, tmp) {
>> 		if (policy == power && tmp_has_capacity &&
>> 			 tmp->flags & sd_flag) {
>> 			sd = tmp;
>> 			//It is fine to got cpu in the domain

			powersaving = 1;

>> 			break;
>> 		}
>> 	}
>>
>> 	while(sd) {
 		if (policy == power && powersaving == 1)
>> 			find_busiest_and_capable_group()
> 
> I'm not sure what find_busiest_and_capable_group() would really be, it
> seems it'll find the busiest and capable group, but isn't it a
> conflict with the first assumption you proposed on your proposal?


This pseudo code missed a power saving workable flag , adding it into
above code should solved your concern.

> 
> Thanks,
> Rakib.


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