linux-kernel - Re: false nr_running check in load balance?

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Date:	Sun, 18 Aug 2013 17:12:36 +0800
From:	Lei Wen <adrian.wenl@...il.com>
To:	Paul Turner <pjt@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Lei Wen <leiwen@...vell.com>
Subject: Re: false nr_running check in load balance?

Paul,

On Tue, Aug 13, 2013 at 5:25 PM, Paul Turner <pjt@...gle.com> wrote:
> On Tue, Aug 13, 2013 at 1:18 AM, Lei Wen <adrian.wenl@...il.com> wrote:
>> Hi Paul,
>>
>> On Tue, Aug 13, 2013 at 4:08 PM, Paul Turner <pjt@...gle.com> wrote:
>>> On Tue, Aug 13, 2013 at 12:38 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>>>> On Tue, Aug 13, 2013 at 12:45:12PM +0800, Lei Wen wrote:
>>>>> > Not quite right; I think you need busiest->cfs.h_nr_running.
>>>>> > cfs.nr_running is the number of entries running in this 'group'. If
>>>>> > you've got nested groups like:
>>>>> >
>>>>> >  'root'
>>>>> >    \
>>>>> >    'A'
>>>>> >    / \
>>>>> >   t1 t2
>>>>> >
>>>>> > root.nr_running := 1 'A', even though you've got multiple running tasks.
>>>>> >
>>>>>
>>>>> You're absolutely right for this. :)
>>>>> I miss it for not considering the group case...
>>>>>
>>>>> Then do you think it is necessary to do below change in load_balance() code?
>>>>>  -       if (busiest->nr_running > 1) {
>>>>>  +       if (busiest->cfs.h_nr_running > 1) {
>>>>>
>>>>
>>>> Yes I think that would be fine.
>>>
>>> If we pivot to use h_nr_running we should probably also update
>>> call-sites such as cpu_load_avg_per_task() for consistency.
>>
>> I didn't find cpu_load_avg_per_task in the latest linux git...
>> Is it a new patch pending while not being submitted?
>
> Transposition typo: cpu_avg_load_per_task()
> More generally: Most things that examine ->nr_running in the fair
> load-balance path.
>

I see...

I have submitted several patches, which covers cpu_avg_load_per_task.
Please help to check them.

Thanks,
Lei
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