linux-kernel - Re: [patch v5 11/15] sched: add power/performance balance allow flag

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Date:	Wed, 20 Feb 2013 21:52:20 +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,
	morten.rasmussen@....com
Subject: Re: [patch v5 11/15] sched: add power/performance balance allow flag

On 02/20/2013 09:37 PM, Peter Zijlstra wrote:
> On Wed, 2013-02-20 at 20:04 +0800, Alex Shi wrote:
> 
>>>> @@ -5195,6 +5197,8 @@ static int load_balance(int this_cpu, struct rq
>>>> *this_rq,
>>>>                 .idle           = idle,
>>>>                 .loop_break     = sched_nr_migrate_break,
>>>>                 .cpus           = cpus,
>>>> +               .power_lb       = 0,
>>>> +               .perf_lb        = 1,
>>>>         };
>>>>  
>>>>         cpumask_copy(cpus, cpu_active_mask);
>>>
>>> This construct allows for the possibility of power_lb=1,perf_lb=1, does
>>> that make sense? Why not have a single balance_policy enumeration?
>>
>> (power_lb == 1 && perf_lb == 1) is incorrect and impossible to have.
>>
>> (power_lb == 0 && perf_lb == 0) is possible and it means there is no any
>> balance on this cpu.
>>
>> So, enumeration is not enough.
> 
> Huh.. both 0 doesn't make any sense either. If there's no balancing, we
> shouldn't be here to begin with.
> 

Um, both 0 means, there is a balance happen, and we think a power
balance is appropriate for this domain, but maybe this group is already
empty, so the cpu is inappropriate to pull a task, than we exit this
time balancing, to wait another cpu from another appropriate group do
balance and pull a task.

-- 
Thanks
    Alex
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