On 9 April 2013 12:38, Alex Shi <alex....@intel.com> wrote: > 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?
I haven't trace that shows this issue but nothing prevent an update to occur while you get values so you can have a mix of old and new values. > Could you explain more for details? Both fields of a new task increase simultaneously but if you get the old value for runnable_avg_period and the new one for runnable_avg_sum, runnable_avg_sum will be greater than runnable_avg_period during this starting phase. The worst case appears 2ms after the creation of the task, runnable_avg_period and runnable_avg_sum should go from 1024 to 2046. So the task_h_load_avg will be 199% of task_h_load If you have runnable_avg_period with 1024 and runnable_avg_sum with 2046. A simple solution is to check that runnable_avg_period is always greater or equal to runnable_avg_sum like i have done in my packing small tasks patches Vincent > > -- > Thanks > Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
