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

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Date:	Tue, 21 Aug 2012 13:05:04 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
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>,
	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>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in scheduler

On 21 August 2012 02:58, Alex Shi <alex.shi@...el.com> wrote:
> On 08/20/2012 11:36 PM, Vincent Guittot wrote:
>
>>> > What you want it to keep track of a per-cpu utilization level (inverse
>>> > of idle-time) and using PJTs per-task runnable avg see if placing the
>>> > new task on will exceed the utilization limit.
>>> >
>>> > I think some of the Linaro people actually played around with this,
>>> > Vincent?
>> Sorry for the late reply but I had almost no network access during last weeks.
>>
>> So Linaro also works on a power aware scheduler as Peter mentioned.
>>
>> Based on previous tests, we have concluded that main drawback of the
>> (now removed) old power scheduler was that we had no way to make
>> difference between short and long running tasks whereas it's a key
>> input (at least for phone) for deciding to pack tasks and for
>> selecting the core on an asymmetric system.
>
>
> It is hard to estimate future in general view point. but from hack
> point, maybe you can add something to hint this from task_struct. :)
>

per-task load tracking patchsets give you a good view of the last dozen of ms

>> One additional key information is the power distribution in the system
>> which can have a finer granularity than current sched_domain
>> description. Peter's proposal was to use a SHARE_POWERLINE flag
>> similarly to flags that already describe if a sched_domain share
>> resources or cpu capacity.
>
>
> Seems I missed this. what's difference with current SD_SHARE_CPUPOWER
> and SD_SHARE_PKG_RESOURCES.

SD_SHARE_CPUPOWER is set in a sched domain at SMT level (sharing some
part of the physical core)
SD_SHARE_PKG_RESOURCES is set at MC level (sharing some resources like
cache and memory access)

>
>>
>> With these 2 new information, we can have a 1st power saving scheduler
>> which spread or packed tasks across core and package
>
>
> Fine, I like to test them on X86, plus SMT and NUMA :)
>
>>
>> Vincent
>
>
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