Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH] sched/cfs: change initial value of runnable_avg | Date | Wed, 24 Jun 2020 17:32:12 +0100 |
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On 24/06/20 16:44, Vincent Guittot wrote: > Some performance regression on reaim benchmark have been raised with > commit 070f5e860ee2 ("sched/fair: Take into account runnable_avg to classify group") > > The problem comes from the init value of runnable_avg which is initialized > with max value. This can be a problem if the newly forked task is finally > a short task because the group of CPUs is wrongly set to overloaded and > tasks are pulled less agressively. > > Set initial value of runnable_avg equals to util_avg to reflect that there > is no waiting time so far. > > Fixes: 070f5e860ee2 ("sched/fair: Take into account runnable_avg to classify group") > Reported-by: kernel test robot <rong.a.chen@intel.com> > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/fair.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 0424a0af5f87..45e467bf42fc 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -806,7 +806,7 @@ void post_init_entity_util_avg(struct task_struct *p) > } > } > > - sa->runnable_avg = cpu_scale; > + sa->runnable_avg = sa->util_avg;
IIRC we didn't go for this initially because hackbench behaved slightly worse with it. Did we end up re-evaluating this? Also, how does this reaim benchmark behave with it? I *think* the table from that regression thread says it behaves better, but I had a hard time parsing it (seems like it got damaged by line wrapping)
Conceptually I'm all for it, so as long as the tests back it up: Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> > if (p->sched_class != &fair_sched_class) { > /*
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