Re: [patch v3 6/8] sched: consider runnable load average in move_tasks

From: Alex Shi
Date: Tue Apr 09 2013 - 06:38:51 EST

On 04/09/2013 04:58 PM, Vincent Guittot wrote:
>>> >> How do you ensure that runnable_avg_period and runnable_avg_sum are
>>> >> coherent ? an update of the statistic can occur in the middle of your
>>> >> sequence.
>> >
>> > Thanks for your question, Vincent!
>> > the runnable_avg_period and runnable_avg_sum, only updated in
>> > __update_entity_runnable_avg().
>> > Yes, I didn't see some locks to ensure the coherent of them. but they
>> > are updated closely, and it is not big deal even a little incorrect to
>> > their value. These data are collected periodically, don't need very very
>> > precise at every time.
>> > Am I right? :)
> The problem mainly appears during starting phase (the 1st 345ms) when
> runnable_avg_period has not reached the max value yet so you can have
> avg.runnable_avg_sum greater than avg.runnable_avg_period. In a worst
> case, runnable_avg_sum could be twice runnable_avg_period

Oh, That's a serious problem. Do you catch it in real word or in code?
Could you explain more for details?

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