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

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Date:	Thu, 16 Aug 2012 14:05:45 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Alex Shi <alex.shi@...el.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 8/16/12, Alex Shi <alex.shi@...el.com> wrote:
> 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.
>
Okay, then what would be the default mechanism? Performance or
powersavings ? Your proposal deals with performance and power saving,
but there should be a default mechanism too, what that default
mechanism would be? Shouldn't  performance be the default one and
discard checking for performance?

>>
>>>
>>> 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.
>
I think I should take a look at this one when it'll be prepared for RFC.

Thanks,
Rakib.
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