The following commit has been merged into the sched/core branch of tip: Commit-ID: 47a861395636ff9477d0d737856f87bd86793ae5 Gitweb: https://git.kernel.org/tip/47a861395636ff9477d0d737856f87bd86793ae5 Author: Valentin Schneider <valentin.schneider@xxxxxxx> AuthorDate: Wed, 07 Apr 2021 23:06:28 +01:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Thu, 08 Apr 2021 23:09:45 +02:00 sched/fair: Introduce a CPU capacity comparison helper During load-balance, groups classified as group_misfit_task are filtered out if they do not pass group_smaller_max_cpu_capacity(<candidate group>, <local group>); which itself employs fits_capacity() to compare the sgc->max_capacity of both groups. Due to the underlying margin, fits_capacity(X, 1024) will return false for any X > 819. Tough luck, the capacity_orig's on e.g. the Pixel 4 are {261, 871, 1024}. If a CPU-bound task ends up on one of those "medium" CPUs, misfit migration will never intentionally upmigrate it to a CPU of higher capacity due to the aforementioned margin. One may argue the 20% margin of fits_capacity() is excessive in the advent of counter-enhanced load tracking (APERF/MPERF, AMUs), but one point here is that fits_capacity() is meant to compare a utilization value to a capacity value, whereas here it is being used to compare two capacity values. As CPU capacity and task utilization have different dynamics, a sensible approach here would be to add a new helper dedicated to comparing CPU capacities. Also note that comparing capacity extrema of local and source sched_group's doesn't make much sense when at the day of the day the imbalance will be pulled by a known env->dst_cpu, whose capacity can be anywhere within the local group's capacity extrema. While at it, replace group_smaller_{min, max}_cpu_capacity() with comparisons of the source group's min/max capacity and the destination CPU's capacity. Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> Reviewed-by: Qais Yousef <qais.yousef@xxxxxxx> Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx> Tested-by: Lingutla Chandrasekhar <clingutla@xxxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20210407220628.3798191-4-valentin.schneider@xxxxxxx --- kernel/sched/fair.c | 33 ++++++++++----------------------- 1 file changed, 10 insertions(+), 23 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3ed436e..f9440ee 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -113,6 +113,13 @@ int __weak arch_asym_cpu_priority(int cpu) */ #define fits_capacity(cap, max) ((cap) * 1280 < (max) * 1024) +/* + * The margin used when comparing CPU capacities. + * is 'cap1' noticeably greater than 'cap2' + * + * (default: ~5%) + */ +#define capacity_greater(cap1, cap2) ((cap1) * 1024 > (cap2) * 1078) #endif #ifdef CONFIG_CFS_BANDWIDTH @@ -8395,26 +8402,6 @@ group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs) return false; } -/* - * group_smaller_min_cpu_capacity: Returns true if sched_group sg has smaller - * per-CPU capacity than sched_group ref. - */ -static inline bool -group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref) -{ - return fits_capacity(sg->sgc->min_capacity, ref->sgc->min_capacity); -} - -/* - * group_smaller_max_cpu_capacity: Returns true if sched_group sg has smaller - * per-CPU capacity_orig than sched_group ref. - */ -static inline bool -group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref) -{ - return fits_capacity(sg->sgc->max_capacity, ref->sgc->max_capacity); -} - static inline enum group_type group_classify(unsigned int imbalance_pct, struct sched_group *group, @@ -8570,7 +8557,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, * internally or be covered by avg_load imbalance (eventually). */ if (sgs->group_type == group_misfit_task && - (!group_smaller_max_cpu_capacity(sg, sds->local) || + (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || sds->local_stat.group_type != group_has_spare)) return false; @@ -8654,7 +8641,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, */ if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && (sgs->group_type <= group_fully_busy) && - (group_smaller_min_cpu_capacity(sds->local, sg))) + (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu)))) return false; return true; @@ -9454,7 +9441,7 @@ static struct rq *find_busiest_queue(struct lb_env *env, * average load. */ if (env->sd->flags & SD_ASYM_CPUCAPACITY && - capacity_of(env->dst_cpu) < capacity && + !capacity_greater(capacity_of(env->dst_cpu), capacity) && nr_running == 1) continue;
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