Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752015AbbHNXEr (ORCPT ); Fri, 14 Aug 2015 19:04:47 -0400 Received: from eu-smtp-delivery-143.mimecast.com ([146.101.78.143]:31907 "EHLO eu-smtp-delivery-143.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750735AbbHNXEq convert rfc822-to-8bit (ORCPT ); Fri, 14 Aug 2015 19:04:46 -0400 Message-ID: <55CE7409.1000700@arm.com> Date: Sat, 15 Aug 2015 00:04:41 +0100 From: Dietmar Eggemann User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0 MIME-Version: 1.0 To: Morten Rasmussen , "peterz@infradead.org" , "mingo@redhat.com" CC: "vincent.guittot@linaro.org" , "daniel.lezcano@linaro.org" , "yuyang.du@intel.com" , "mturquette@baylibre.com" , "rjw@rjwysocki.net" , Juri Lelli , "sgurrappadi@nvidia.com" , "pang.xunlei@zte.com.cn" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 3/6] sched/fair: Make utilization tracking cpu scale-invariant References: <1439569394-11974-1-git-send-email-morten.rasmussen@arm.com> <1439569394-11974-4-git-send-email-morten.rasmussen@arm.com> In-Reply-To: <1439569394-11974-4-git-send-email-morten.rasmussen@arm.com> X-OriginalArrivalTime: 14 Aug 2015 23:04:43.0335 (UTC) FILETIME=[9B321570:01D0D6E5] X-MC-Unique: KfshbH45R2KxtjQIJQEwdQ-1 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5380 Lines: 133 On 14/08/15 17:23, Morten Rasmussen wrote: > From: Dietmar Eggemann [...] > @@ -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); There is a small issue (using = instead of +=) with fatal consequences for the utilization signal. -- >8 -- Subject: [PATCH] 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. Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Dietmar Eggemann Signed-off-by: Morten Rasmussen --- include/linux/sched.h | 2 +- kernel/sched/fair.c | 7 ++++--- kernel/sched/sched.h | 2 +- 3 files changed, 6 insertions(+), 5 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index a15305117ace..78a93d716fcb 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1180,7 +1180,7 @@ struct load_weight { * 1) load_avg factors frequency scaling into the amount of time that a * sched_entity is runnable on a rq into its weight. For cfs_rq, it is the * aggregated such weights of all runnable and blocked sched_entities. - * 2) util_avg factors frequency scaling into the amount of time + * 2) util_avg factors frequency and cpu scaling into the amount of time * that a sched_entity is running on a CPU, in the range [0..SCHED_LOAD_SCALE]. * For cfs_rq, it is the aggregated such times of all runnable and * blocked sched_entities. diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c72223a299a8..3321eb13e422 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 7e6f2506a402..50836a9301f9 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1406,7 +1406,7 @@ 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; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/