linux-kernel - Re: [RFC 2/2] sched/fair: prefer a CPU in the "lowest" idle state

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Message-ID: <87pq0lu7ew.fsf@sejong.aot.lge.com>
Date:	Thu, 31 Jan 2013 16:40:39 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de
Subject: Re: [RFC 2/2] sched/fair: prefer a CPU in the "lowest" idle state

On Thu, 31 Jan 2013 15:30:02 +0800, Michael Wang wrote:
> On 01/31/2013 02:58 PM, Namhyung Kim wrote:
>> But AFAIK the number of states in cpuidle is usually less than 10 so maybe
>> we can change the weight then, but there's no promise...
>
> And I just got another case we should take care:
>
> 	group 0		cpu 0			cpu 1
> 			power index 8		power index 8
>
>
> 	group 1		cpu 2			cpu 3
> 			power index 0		load 15
>
> so load of group 0 is 16 and group 1 is 15, but group 0 is better...

Maybe it's not.  The cpus in group 0 are in a lower power state so that
there will be a benefit to select cpu 2 from the power' PoV IMHO.  Also
such a low power state has a longer exit latency so that we should
choose cpu2 to get a better performance and it's the basic idea of this
patchset I believe.

Thanks,
Namhyung
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