4.18-stable review patch. If anyone has any objections, please let me know.
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From: Quentin Perret quentin.perret@arm.com
[ Upstream commit 8fe5c5a937d0f4e84221631833a2718afde52285 ]
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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/fair.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -735,11 +735,12 @@ static void attach_entity_cfs_rq(struct * To solve this problem, we also cap the util_avg of successive tasks to * only 1/2 of the left utilization budget: * - * util_avg_cap = (1024 - cfs_rq->avg.util_avg) / 2^n + * util_avg_cap = (cpu_scale - cfs_rq->avg.util_avg) / 2^n * - * where n denotes the nth task. + * where n denotes the nth task and cpu_scale the CPU capacity. * - * For example, a simplest series from the beginning would be like: + * For example, for a CPU with 1024 of capacity, a simplest series from + * the beginning would be like: * * task util_avg: 512, 256, 128, 64, 32, 16, 8, ... * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ... @@ -751,7 +752,8 @@ void post_init_entity_util_avg(struct sc { struct cfs_rq *cfs_rq = cfs_rq_of(se); struct sched_avg *sa = &se->avg; - long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2; + long cpu_scale = arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq))); + long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2;
if (cap > 0) { if (cfs_rq->avg.util_avg != 0) {