From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753574AbbGWOWc (ORCPT ); Thu, 23 Jul 2015 10:22:32 -0400 Received: from mail-pd0-f174.google.com ([209.85.192.174]:33777 "EHLO mail-pd0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752906AbbGWOW0 (ORCPT ); Thu, 23 Jul 2015 10:22:26 -0400 Date: Thu, 23 Jul 2015 22:22:16 +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: <20150723142216.GA21773@leoy-linaro> References: <1436293469-25707-2-git-send-email-morten.rasmussen@arm.com> <20150721154145.GA23852@leoy-linaro> <20150722133103.GA21785@e105550-lin.cambridge.arm.com> <20150722145904.GA18354@leoy-linaro> <20150723110626.GC21785@e105550-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150723110626.GC21785@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 Thu, Jul 23, 2015 at 12:06:26PM +0100, Morten Rasmussen wrote: > On Wed, Jul 22, 2015 at 10:59:04PM +0800, Leo Yan wrote: > > 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. > > Yes. We have patches for arm64 if you are interested. We are using them > for the Juno platforms. If convenience, please share with me related patches, so i can directly apply them and do some profiling works. > > 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 is the idea with the notifiers. If the architecture code a specific > architecture wants to be poked by cpufreq when the frequency is changed > it should have a way to subscribe to those. Another way of implementing > it is to let the architecture code call a helper function in cpufreq > every time the scheduler calls into the architecture code to get the > scaling factor (arch_scale_freq_capacity()). We actually did it that way > a couple of versions back using weak functions. It wasn't as clean as > using the notifiers, but if we make the necessary changes to cpufreq to > let the architecture code call into cpufreq that could be even better. > > > > > > 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? > > The issue is first of all to define what 100% means. Is it > policy->cur/policy->max or policy->cur/uncapped_max? Where uncapped max > is the max frequency supported by the hardware when not capped in any > way by governors or thermal framework. > > If we choose the first definition then we have to recalculate the cpu > capacity scaling factor (arch_scale_cpu_capacity()) too whenever > policy->max changes such that capacity_orig is updated appropriately. > > The scale-invariance code in the scheduler assumes: > > arch_scale_cpu_capacity()*arch_scale_freq_capacity() = current capacity This is an important concept, thanks for the explaining. > ...and that capacity_orig = arch_scale_cpu_capacity() is the max > available capacity. If we cap the frequency to say, 50%, by setting > policy->max then we have to reduce arch_scale_cpu_capacity() to 50% to > still get the right current capacity using the expression above. > > Using the second definition arch_scale_cpu_capacity() can be a static > value and arch_scale_freq_capacity() is always relative to uncapped_max. > It seems simpler, but capacity_orig could then be an unavailable > capacity and hence we would need to introduce a third capacity to track > the current max capacity and use that for scheduling decisions. > As you have already discovered the current code is a combination of both > which is broken when policy->max is reduced. > > Thinking more about it, I would suggest to go with the first definition. > The scheduler doesn't need to know about currently unavailable compute > capacity it should balance based on the current situation, so it seems > to make sense to let capacity_orig reflect the current max capacity. Agree. > I would suggest that we fix arch_scale_cpu_capacity() to take > policy->max changes into account. We need to know the uncapped max > frequency somehow to do that. I haven't looked into if we can get that > from cpufreq. Also, we need to make sure that no load-balance code > assumes that cpus have a capacity of 1024. Cpufreq framework provides API *cpufreq_quick_get_max()* and *cpufreq_quick_get()* for inquiry current frequency and max frequency, but i'm curious if these two functions can be directly called by scheduler, due they acquire and release locks internally. Thanks, Leo Yan