Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | Re: [PATCH] sched/fair: Remove the duplicate check from group_has_capacity() | Date | Mon, 10 Aug 2020 19:33:20 +0100 |
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On 10/08/20 02:00, Qi Zheng wrote: > 1. The group_has_capacity() function is only called in > group_classify(). > 2. The following inequality has already been checked in > group_is_overloaded() which was also called in > group_classify(). > > (sgs->group_capacity * imbalance_pct) < > (sgs->group_runnable * 100) >
Consider group_is_overloaded() returns false because of the first condition:
if (sgs->sum_nr_running <= sgs->group_weight) return false;
then group_has_capacity() would be the first place where the group_runnable vs group_capacity comparison would be done.
Now in that specific case we'll actually only check it if
sgs->sum_nr_running == sgs->group_weight
and the only case where the runnable vs capacity check can fail here is if there's significant capacity pressure going on. TBH this capacity pressure could be happening even when there are fewer tasks than CPUs, so I'm not sure how intentional that corner case is.
For the
sgs->sum_nr_running > sgs->group_weight
case I agree with your patch, there just is that oddity at the == case.
> So just remove the duplicate check from group_has_capacity(). > > Signed-off-by: Qi Zheng <arch0.zheng@gmail.com> > --- > kernel/sched/fair.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 2ba8f230feb9..a41903fb327a 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8234,10 +8234,6 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs) > if (sgs->sum_nr_running < sgs->group_weight) > return true; > > - if ((sgs->group_capacity * imbalance_pct) < > - (sgs->group_runnable * 100)) > - return false; > - > if ((sgs->group_capacity * 100) > > (sgs->group_util * imbalance_pct)) > return true;
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