From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934389AbbGVO7P (ORCPT ); Wed, 22 Jul 2015 10:59:15 -0400 Received: from mail-pa0-f50.google.com ([209.85.220.50]:34975 "EHLO mail-pa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933142AbbGVO7N (ORCPT ); Wed, 22 Jul 2015 10:59:13 -0400 Date: Wed, 22 Jul 2015 22:59:04 +0800 From: Leo Yan To: Morten Rasmussen Cc: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org, daniel.lezcano@linaro.org, Dietmar Eggemann , 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, linux-pm@vger.kernel.org, Russell King Subject: Re: [RFCv5, 01/46] arm: Frequency invariant scheduler load-tracking support Message-ID: <20150722145904.GA18354@leoy-linaro> References: <1436293469-25707-2-git-send-email-morten.rasmussen@arm.com> <20150721154145.GA23852@leoy-linaro> <20150722133103.GA21785@e105550-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150722133103.GA21785@e105550-lin.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 22, 2015 at 02:31:04PM +0100, Morten Rasmussen wrote: > On Tue, Jul 21, 2015 at 11:41:45PM +0800, Leo Yan wrote: > > Hi Morten, > > > > On Tue, Jul 07, 2015 at 07:23:44PM +0100, Morten Rasmussen wrote: > > > From: Morten Rasmussen > > > > > > Implements arch-specific function to provide the scheduler with a > > > frequency scaling correction factor for more accurate load-tracking. > > > The factor is: > > > > > > current_freq(cpu) << SCHED_CAPACITY_SHIFT / max_freq(cpu) > > > > > > This implementation only provides frequency invariance. No cpu > > > invariance yet. > > > > > > Cc: Russell King > > > > > > Signed-off-by: Morten Rasmussen > > > > > > --- > > > arch/arm/include/asm/topology.h | 7 +++++ > > > arch/arm/kernel/smp.c | 57 +++++++++++++++++++++++++++++++++++++++-- > > > arch/arm/kernel/topology.c | 17 ++++++++++++ > > > 3 files changed, 79 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h > > > index 370f7a7..c31096f 100644 > > > --- a/arch/arm/include/asm/topology.h > > > +++ b/arch/arm/include/asm/topology.h > > > @@ -24,6 +24,13 @@ void init_cpu_topology(void); > > > void store_cpu_topology(unsigned int cpuid); > > > const struct cpumask *cpu_coregroup_mask(int cpu); > > > > > > +#define arch_scale_freq_capacity arm_arch_scale_freq_capacity > > > +struct sched_domain; > > > +extern > > > +unsigned long arm_arch_scale_freq_capacity(struct sched_domain *sd, int cpu); > > > + > > > +DECLARE_PER_CPU(atomic_long_t, cpu_freq_capacity); > > > + > > > #else > > > > > > static inline void init_cpu_topology(void) { } > > > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > > > index cca5b87..a32539c 100644 > > > --- a/arch/arm/kernel/smp.c > > > +++ b/arch/arm/kernel/smp.c > > > @@ -677,12 +677,34 @@ static DEFINE_PER_CPU(unsigned long, l_p_j_ref); > > > static DEFINE_PER_CPU(unsigned long, l_p_j_ref_freq); > > > static unsigned long global_l_p_j_ref; > > > static unsigned long global_l_p_j_ref_freq; > > > +static DEFINE_PER_CPU(atomic_long_t, cpu_max_freq); > > > +DEFINE_PER_CPU(atomic_long_t, cpu_freq_capacity); > > > + > > > +/* > > > + * Scheduler load-tracking scale-invariance > > > + * > > > + * Provides the scheduler with a scale-invariance correction factor that > > > + * compensates for frequency scaling through arch_scale_freq_capacity() > > > + * (implemented in topology.c). > > > + */ > > > +static inline > > > +void scale_freq_capacity(int cpu, unsigned long curr, unsigned long max) > > > +{ > > > + unsigned long capacity; > > > + > > > + if (!max) > > > + return; > > > + > > > + capacity = (curr << SCHED_CAPACITY_SHIFT) / max; > > > + atomic_long_set(&per_cpu(cpu_freq_capacity, cpu), capacity); > > > +} > > > > > > static int cpufreq_callback(struct notifier_block *nb, > > > unsigned long val, void *data) > > > { > > > struct cpufreq_freqs *freq = data; > > > int cpu = freq->cpu; > > > + unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu)); > > > > > > if (freq->flags & CPUFREQ_CONST_LOOPS) > > > return NOTIFY_OK; > > > @@ -707,6 +729,10 @@ static int cpufreq_callback(struct notifier_block *nb, > > > per_cpu(l_p_j_ref_freq, cpu), > > > freq->new); > > > } > > > + > > > + if (val == CPUFREQ_PRECHANGE) > > > + scale_freq_capacity(cpu, freq->new, max); > > > + > > > return NOTIFY_OK; > > > } > > > > > > @@ -714,11 +740,38 @@ static struct notifier_block cpufreq_notifier = { > > > .notifier_call = cpufreq_callback, > > > }; > > > > > > +static int cpufreq_policy_callback(struct notifier_block *nb, > > > + unsigned long val, void *data) > > > +{ > > > + struct cpufreq_policy *policy = data; > > > + int i; > > > + > > > + if (val != CPUFREQ_NOTIFY) > > > + return NOTIFY_OK; > > > + > > > + for_each_cpu(i, policy->cpus) { > > > + scale_freq_capacity(i, policy->cur, policy->max); > > > + atomic_long_set(&per_cpu(cpu_max_freq, i), policy->max); > > > + } > > > + > > > + return NOTIFY_OK; > > > +} > > > + > > > +static struct notifier_block cpufreq_policy_notifier = { > > > + .notifier_call = cpufreq_policy_callback, > > > +}; > > > + > > > static int __init register_cpufreq_notifier(void) > > > { > > > - return cpufreq_register_notifier(&cpufreq_notifier, > > > + int ret; > > > + > > > + ret = cpufreq_register_notifier(&cpufreq_notifier, > > > CPUFREQ_TRANSITION_NOTIFIER); > > > + if (ret) > > > + return ret; > > > + > > > + return cpufreq_register_notifier(&cpufreq_policy_notifier, > > > + CPUFREQ_POLICY_NOTIFIER); > > > } > > > core_initcall(register_cpufreq_notifier); > > > > For "cpu_freq_capacity" structure, could move it into driver/cpufreq > > so that it can be shared by all architectures? Otherwise, every > > architecture's smp.c need register notifier for themselves. > > We could, but I put it in arch/arm/* as not all architectures might want > this notifier. The frequency scaling factor could be provided based on > architecture specific performance counters instead. AFAIK, the Intel > p-state driver does not even fire the notifiers so the notifier > solution would be redundant code for those platforms. When i tried to enable EAS on Hikey, i found it's absent related code for arm64; actually this code section can also be reused by arm64, so just brought up this question. Just now roughly went through the driver "drivers/cpufreq/intel_pstate.c"; that's true it has different implementation comparing to usual ARM SoCs. So i'd like to ask this question with another way: should cpufreq framework provides helper functions for getting related cpu frequency scaling info? If the architecture has specific performance counters then it can ignore these helper functions. > That said, the above solution is not handling changes to policy->max > very well. Basically, we don't inform the scheduler if it has changed > which means that the OPP represented by "100%" might change. We need > cpufreq to keep track of the true max frequency when policy->max is > changed to work out the correct scaling factor instead of having it > relative to policy->max. i'm not sure understand correctly here. For example, when thermal framework limits the cpu frequency, it will update the value for policy->max, so scheduler will get the correct scaling factor, right? So i don't know what's the issue at here. Further more, i noticed in the later patches for arch_scale_cpu_capacity(); the cpu capacity is calculated by the property passed by DT, so it's a static value. In some cases, system may constraint the maximum frequency for CPUs, so in this case, will scheduler get misknowledge from arch_scale_cpu_capacity after system has imposed constraint for maximum frequency? Sorry if these questions have been discussed before :) Thanks, Leo Yan