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From: Namhyung Kim <namhyung@kernel.org>
To: Michael Wang <wangyun@linux.vnet.ibm.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        linux-kernel@vger.kernel.org,
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        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        tglx@linutronix.de
Subject: Re: [RFC 2/2] sched/fair: prefer a CPU in the "lowest" idle state
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Date: Thu, 31 Jan 2013 16:40:39 +0900
In-Reply-To: <510A1D7A.3050408@linux.vnet.ibm.com> (Michael Wang's message of
	"Thu, 31 Jan 2013 15:30:02 +0800")
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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