On 9 April 2013 10:05, Alex Shi <alex....@intel.com> wrote: > On 04/09/2013 03:08 PM, Vincent Guittot wrote: >> On 2 April 2013 05:23, Alex Shi <alex....@intel.com> wrote: >>> Except using runnable load average in background, move_tasks is also >>> the key functions in load balance. We need consider the runnable load >>> average in it in order to the apple to apple load comparison. >>> >>> Signed-off-by: Alex Shi <alex....@intel.com> >>> --- >>> kernel/sched/fair.c | 11 ++++++++++- >>> 1 file changed, 10 insertions(+), 1 deletion(-) >>> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>> index 1f9026e..bf4e0d4 100644 >>> --- a/kernel/sched/fair.c >>> +++ b/kernel/sched/fair.c >>> @@ -3966,6 +3966,15 @@ static unsigned long task_h_load(struct task_struct >>> *p); >>> >>> static const unsigned int sched_nr_migrate_break = 32; >>> >>> +static unsigned long task_h_load_avg(struct task_struct *p) >>> +{ >>> + u32 period = p->se.avg.runnable_avg_period; >>> + if (!period) >>> + return 0; >>> + >>> + return task_h_load(p) * p->se.avg.runnable_avg_sum / period; >> >> 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 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/