linux-kernel - Re: [patch v4 03/18] sched: fix find_idlest

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Date:	Tue, 12 Feb 2013 11:16:48 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	torvalds@...ux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v4 03/18] sched: fix find_idlest_group mess logical

On Thu, 2013-01-24 at 11:06 +0800, Alex Shi wrote:
> There is 4 situations in the function:
> 1, no task allowed group;
> 	so min_load = ULONG_MAX, this_load = 0, idlest = NULL
> 2, only local group task allowed;
> 	so min_load = ULONG_MAX, this_load assigned, idlest = NULL
> 3, only non-local task group allowed;
> 	so min_load assigned, this_load = 0, idlest != NULL
> 4, local group + another group are task allowed.
> 	so min_load assigned, this_load assigned, idlest != NULL
> 
> Current logical will return NULL in first 3 kinds of scenarios.
> And still return NULL, if idlest group is heavier then the
> local group in the 4th situation.
> 
> Actually, I thought groups in situation 2,3 are also eligible to host
> the task. And in 4th situation, agree to bias toward local group.

I'm not convinced this is actually a cleanup.. taken together with patch
4 (which is a direct consequence of this patch afaict) you replace one
conditional with 2.

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