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

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Message-ID: <511BAC40.6080009@intel.com>
Date:	Wed, 13 Feb 2013 23:07:44 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 02/12/2013 06:16 PM, Peter Zijlstra wrote:
> 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.
> 

The current logical will always miss the eligible CPU in the 3rd
situation.  'sd = sd->child' still skip the non-local group eligible CPU.


-- 
Thanks
    Alex
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