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

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Date:	Sat, 02 Feb 2013 18:50:05 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
CC:	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 01/31/2013 03:12 AM, Michael Wang wrote:
> I'm not sure, but just concern about this case:
> 
> 	group 0		cpu 0			cpu 1
> 			least idle		4 task
> 
> 	group 1		cpu 2			cpu 3
> 			1 task			1 task
> 
> The previous logical will pick group 1 and now it will take group 0, and
> that cause more imbalance, doesn't it?

That depends on load of CPU 0 + 1 vs CPU 2 + 3. If the four tasks on
CPU1 are idle then the previous code should return group 0.
If the four tasks are running at 100% each then two of them should be
migrated to CPU0 and this point the idle state does not matter :)

> May be check that state in find_idlest_cpu() will be better?

You say to move this from find_idlest_group() to find_idlest_cpu()?

> Regards,
> Michael Wang

Sebastian
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