Messages in this thread |  | | From | Valentin Schneider <> | Subject | Re: [PATCH 3/8] sched/fair: Tweak misfit-related capacity checks | Date | Fri, 05 Feb 2021 20:07:08 +0000 |
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On 05/02/21 18:17, Vincent Guittot wrote: > On Fri, 5 Feb 2021 at 18:00, Valentin Schneider >> >> @@ -8253,7 +8260,7 @@ check_cpu_capacity(struct rq *rq, struct sched_domain *sd) >> >> static inline int check_misfit_status(struct rq *rq, struct sched_domain *sd) >> >> { >> >> return rq->misfit_task_load && >> >> - (rq->cpu_capacity_orig < rq->rd->max_cpu_capacity || >> >> + (capacity_greater(rq->rd->max_cpu_capacity, rq->cpu_capacity_orig) || >> > >> > Why do you add a margin here whereas there was no margin before ? >> > >> >> Comparing capacities without any sort of filter can lead to ping-ponging >> tasks around (capacity values very easily fluctuate by +/- 1, if not more). > > max_cpu_capacity reflects the max of the cpu_capacity_orig values > don't aim to change and can be considered as static values. > It would be better to fix this rounding problem (if any) in > topology_get_cpu_scale instead of computing a margin every time it's > used >
That's embarrassing, I was convinced we had something updating rd->max_cpu_capacity with actual rq->capacity values... But as you point out that's absolutely not the case, it's all based on rq->capacity_orig, which completely invalidates patch 5/8.
Welp.
Perhaps I can still keep 5/8 with something like
if (!rq->misfit_task_load) return false;
do { if (capacity_greater(group->sgc->max_capacity, rq->cpu_capacity)) return true;
group = group->next; } while (group != sd->groups);
return false;
This works somewhat well for big.LITTLE, but for DynamIQ systems under a single L3 this ends up iterating over all the CPUs :/
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