Re: [PATCH] sched: fix incorrect PELT values on SMT
From: Wanpeng Li <hidden>
Date: 2016-08-19 02:30:49
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lkml
2016-08-19 9:55 GMT+08:00 Steve Muckle [off-list ref]:
PELT scales its util_sum and util_avg values via arch_scale_cpu_capacity(). If that function is passed the CPU's sched domain then it will reduce the scaling capacity if SD_SHARE_CPUCAPACITY is set. PELT does not pass in the sd however. The other caller of arch_scale_cpu_capacity, update_cpu_capacity(), does. This means util_sum and util_avg scale beyond the CPU capacity on SMT. On an Intel i7-3630QM for example rq->cpu_capacity_orig is 589 but util_avg scales up to 1024. Fix this by passing in the sd in __update_load_avg() as well.
I believe we notice this at least several months ago. https://lkml.org/lkml/2016/5/25/228
quoted hunk ↗ jump to hunk
Signed-off-by: Steve Muckle <redacted> --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 61d485421bed..95d34b337152 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c@@ -2731,7 +2731,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, sa->last_update_time = now; scale_freq = arch_scale_freq_capacity(NULL, cpu); - scale_cpu = arch_scale_cpu_capacity(NULL, cpu); + scale_cpu = arch_scale_cpu_capacity(cpu_rq(cpu)->sd, cpu); /* delta_w is the amount already accumulated against our next period */ delta_w = sa->period_contrib; --2.7.3
-- Regards, Wanpeng Li