From e3279a2e6d697e00e74f905851ee7cf532f72b2d Mon Sep 17 00:00:00 2001 From: Dietmar Eggemann Date: Sat, 15 Aug 2015 00:04:41 +0100 Subject: sched/fair: Make utilization tracking CPU scale-invariant Besides the existing frequency scale-invariance correction factor, apply CPU scale-invariance correction factor to utilization tracking to compensate for any differences in compute capacity. This could be due to micro-architectural differences (i.e. instructions per seconds) between cpus in HMP systems (e.g. big.LITTLE), and/or differences in the current maximum frequency supported by individual cpus in SMP systems. In the existing implementation utilization isn't comparable between cpus as it is relative to the capacity of each individual CPU. Each segment of the sched_avg.util_sum geometric series is now scaled by the CPU performance factor too so the sched_avg.util_avg of each sched entity will be invariant from the particular CPU of the HMP/SMP system on which the sched entity is scheduled. With this patch, the utilization of a CPU stays relative to the max CPU performance of the fastest CPU in the system. In contrast to utilization (sched_avg.util_sum), load (sched_avg.load_sum) should not be scaled by compute capacity. The utilization metric is based on running time which only makes sense when cpus are _not_ fully utilized (utilization cannot go beyond 100% even if more tasks are added), where load is runnable time which isn't limited by the capacity of the CPU and therefore is a better metric for overloaded scenarios. If we run two nice-0 busy loops on two cpus with different compute capacity their load should be similar since their compute demands are the same. We have to assume that the compute demand of any task running on a fully utilized CPU (no spare cycles = 100% utilization) is high and the same no matter of the compute capacity of its current CPU, hence we shouldn't scale load by CPU capacity. Signed-off-by: Dietmar Eggemann Signed-off-by: Morten Rasmussen Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/55CE7409.1000700@arm.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 7 ++++--- kernel/sched/sched.h | 2 +- 2 files changed, 5 insertions(+), 4 deletions(-) (limited to 'kernel') diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 102cdf1e4e97..573dc98c6248 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2553,6 +2553,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, u32 contrib; int delta_w, scaled_delta_w, decayed = 0; unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu); + unsigned long scale_cpu = arch_scale_cpu_capacity(NULL, cpu); delta = now - sa->last_update_time; /* @@ -2596,7 +2597,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, } } if (running) - sa->util_sum += scaled_delta_w; + sa->util_sum += scale(scaled_delta_w, scale_cpu); delta -= delta_w; @@ -2620,7 +2621,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, cfs_rq->runnable_load_sum += weight * contrib; } if (running) - sa->util_sum += contrib; + sa->util_sum += scale(contrib, scale_cpu); } /* Remainder of delta accrued against u_0` */ @@ -2631,7 +2632,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, cfs_rq->runnable_load_sum += weight * scaled_delta; } if (running) - sa->util_sum += scaled_delta; + sa->util_sum += scale(scaled_delta, scale_cpu); sa->period_contrib += delta; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c0726d5fd6a3..167ab4844ee6 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1398,7 +1398,7 @@ unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu) static __always_inline unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu) { - if ((sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1)) + if (sd && (sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1)) return sd->smt_gain / sd->span_weight; return SCHED_CAPACITY_SCALE; -- cgit v1.2.3