sched/fair: Fix util_avg of new tasks for asymmetric systems
When a new task wakes-up for the first time, its initial utilization is set to half of the spare capacity of its CPU. The current implementation of post_init_entity_util_avg() uses SCHED_CAPACITY_SCALE directly as a capacity reference. As a result, on a big.LITTLE system, a new task waking up on an idle little CPU will be given ~512 of util_avg, even if the CPU's capacity is significantly less than that. Fix this by computing the spare capacity with arch_scale_cpu_capacity(). Signed-off-by: Quentin Perret <quentin.perret@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Vincent Guittot <vincent.guittot@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dietmar.eggemann@arm.com Cc: morten.rasmussen@arm.com Cc: patrick.bellasi@arm.com Link: http://lkml.kernel.org/r/20180612112215.25448-1-quentin.perret@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -735,11 +735,12 @@ static void attach_entity_cfs_rq(struct sched_entity *se);
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* To solve this problem, we also cap the util_avg of successive tasks to
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* To solve this problem, we also cap the util_avg of successive tasks to
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* only 1/2 of the left utilization budget:
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* only 1/2 of the left utilization budget:
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*
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*
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* util_avg_cap = (1024 - cfs_rq->avg.util_avg) / 2^n
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* util_avg_cap = (cpu_scale - cfs_rq->avg.util_avg) / 2^n
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*
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*
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* where n denotes the nth task.
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* where n denotes the nth task and cpu_scale the CPU capacity.
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*
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*
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* For example, a simplest series from the beginning would be like:
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* For example, for a CPU with 1024 of capacity, a simplest series from
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* the beginning would be like:
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*
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*
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* task util_avg: 512, 256, 128, 64, 32, 16, 8, ...
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* task util_avg: 512, 256, 128, 64, 32, 16, 8, ...
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* cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ...
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* cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ...
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@ -751,7 +752,8 @@ void post_init_entity_util_avg(struct sched_entity *se)
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{
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{
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struct cfs_rq *cfs_rq = cfs_rq_of(se);
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struct cfs_rq *cfs_rq = cfs_rq_of(se);
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struct sched_avg *sa = &se->avg;
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struct sched_avg *sa = &se->avg;
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long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
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long cpu_scale = arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq)));
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long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2;
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if (cap > 0) {
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if (cap > 0) {
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if (cfs_rq->avg.util_avg != 0) {
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if (cfs_rq->avg.util_avg != 0) {
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