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Tue, 30 Jan 2024 14:09:35 -0800 (PST) Received: from airbuntu ([213.122.231.14]) by smtp.gmail.com with ESMTPSA id k7-20020a05600c1c8700b0040ef3ae26cdsm8878492wms.37.2024.01.30.14.09.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Jan 2024 14:09:34 -0800 (PST) Date: Tue, 30 Jan 2024 22:09:32 +0000 From: Qais Yousef To: Vincent Guittot Cc: linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org, sudeep.holla@arm.com, rafael@kernel.org, viresh.kumar@linaro.org, agross@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, lukasz.luba@arm.com, rui.zhang@intel.com, mhiramat@kernel.org, daniel.lezcano@linaro.org, amit.kachhap@gmail.com, corbet@lwn.net, gregkh@linuxfoundation.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v4 2/5] sched: Take cpufreq feedback into account Message-ID: <20240130220932.2wvnscmzqadmsrd2@airbuntu> References: <20240109164655.626085-1-vincent.guittot@linaro.org> <20240109164655.626085-3-vincent.guittot@linaro.org> <20240130002652.ipdyqs3sjy6qqt6t@airbuntu> <20240130005028.vbqg27ctmanxsej6@airbuntu> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 01/30/24 10:35, Vincent Guittot wrote: > On Tue, 30 Jan 2024 at 01:50, Qais Yousef wrote: > > > > On 01/30/24 00:26, Qais Yousef wrote: > > > On 01/09/24 17:46, Vincent Guittot wrote: > > > > Aggregate the different pressures applied on the capacity of CPUs and > > > > create a new function that returns the actual capacity of the CPU: > > > > get_actual_cpu_capacity() > > > > > > > > Signed-off-by: Vincent Guittot > > > > Reviewed-by: Lukasz Luba > > > > --- > > > > kernel/sched/fair.c | 45 +++++++++++++++++++++++++-------------------- > > > > 1 file changed, 25 insertions(+), 20 deletions(-) > > > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > > index 9cc20855dc2b..e54bbf8b4936 100644 > > > > --- a/kernel/sched/fair.c > > > > +++ b/kernel/sched/fair.c > > > > @@ -4910,13 +4910,22 @@ static inline void util_est_update(struct cfs_rq *cfs_rq, > > > > trace_sched_util_est_se_tp(&p->se); > > > > } > > > > > > > > +static inline unsigned long get_actual_cpu_capacity(int cpu) > > > > +{ > > > > + unsigned long capacity = arch_scale_cpu_capacity(cpu); > > > > + > > > > + capacity -= max(thermal_load_avg(cpu_rq(cpu)), cpufreq_get_pressure(cpu)); > > > > > > Does cpufreq_get_pressure() reflect thermally throttled frequency, or just the > > > policy->max being capped by user etc? I didn't see an update to cpufreq when we > > > topology_update_hw_pressure(). Not sure if it'll go through another path. > > > > It is done via the cooling device. And assume any limitations on freq due to > > power etc are assumed to always to cause the policy->max to change. > > > > (sorry if I missed earlier discussions about this) > > I assume that you have answered all your questions. > > We have now 2 distinct signals: > - hw high freq update which is averaged with PELT and go through > topology_update_hw_pressure > - cpufreq pressure which is not averaged (including cpufreq cooling > device with patch 3) Yes. I think a comment like suggested below is useful to help keeping the code understandable to new comers. But FWIW Reviewed-by: Qais Yousef > > > > > > > > > maxing with thermal_load_avg() will change the behavior below where we used to > > > compare against instantaneous pressure. The concern was that it not just can > > > appear quickly, but disappear quickly too. thermal_load_avg() will decay > > > slowly, no? This means we'll lose a lot of opportunities for better task > > > placement until this decays which can take relatively long time. > > > > > > So maxing handles the direction where a pressure suddenly appears. But it > > > doesn't handle where it disappears. > > > > > > I suspect your thoughts are that if it was transient then thermal_load_avg() > > > should be small anyway - which I think makes sense. > > > > > > I think we need a comment to explain these nuance differences. > > > > > > > + > > > > + return capacity; > > > > +} > > > > + > > > > static inline int util_fits_cpu(unsigned long util, > > > > unsigned long uclamp_min, > > > > unsigned long uclamp_max, > > > > int cpu) > > > > { > > > > - unsigned long capacity_orig, capacity_orig_thermal; > > > > unsigned long capacity = capacity_of(cpu); > > > > + unsigned long capacity_orig; > > > > bool fits, uclamp_max_fits; > > > > > > > > /* > > > > @@ -4948,7 +4957,6 @@ static inline int util_fits_cpu(unsigned long util, > > > > * goal is to cap the task. So it's okay if it's getting less. > > > > */ > > > > capacity_orig = arch_scale_cpu_capacity(cpu); > > > > - capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu); > > > > > > > > /* > > > > * We want to force a task to fit a cpu as implied by uclamp_max. > > > > @@ -5023,7 +5031,8 @@ static inline int util_fits_cpu(unsigned long util, > > > > * handle the case uclamp_min > uclamp_max. > > > > */ > > > > uclamp_min = min(uclamp_min, uclamp_max); > > > > - if (fits && (util < uclamp_min) && (uclamp_min > capacity_orig_thermal)) > > > > + if (fits && (util < uclamp_min) && > > > > + (uclamp_min > get_actual_cpu_capacity(cpu))) > > > > return -1; > > > > > > > > return fits; > > > > @@ -7404,7 +7413,7 @@ select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target) > > > > * Look for the CPU with best capacity. > > > > */ > > > > else if (fits < 0) > > > > - cpu_cap = arch_scale_cpu_capacity(cpu) - thermal_load_avg(cpu_rq(cpu)); > > > > + cpu_cap = get_actual_cpu_capacity(cpu); > > > > > > > > /* > > > > * First, select CPU which fits better (-1 being better than 0). > > > > @@ -7897,8 +7906,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > > > struct root_domain *rd = this_rq()->rd; > > > > int cpu, best_energy_cpu, target = -1; > > > > int prev_fits = -1, best_fits = -1; > > > > - unsigned long best_thermal_cap = 0; > > > > - unsigned long prev_thermal_cap = 0; > > > > + unsigned long best_actual_cap = 0; > > > > + unsigned long prev_actual_cap = 0; > > > > struct sched_domain *sd; > > > > struct perf_domain *pd; > > > > struct energy_env eenv; > > > > @@ -7928,7 +7937,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > > > > > > > for (; pd; pd = pd->next) { > > > > unsigned long util_min = p_util_min, util_max = p_util_max; > > > > - unsigned long cpu_cap, cpu_thermal_cap, util; > > > > + unsigned long cpu_cap, cpu_actual_cap, util; > > > > long prev_spare_cap = -1, max_spare_cap = -1; > > > > unsigned long rq_util_min, rq_util_max; > > > > unsigned long cur_delta, base_energy; > > > > @@ -7940,18 +7949,17 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > > > if (cpumask_empty(cpus)) > > > > continue; > > > > > > > > - /* Account thermal pressure for the energy estimation */ > > > > + /* Account external pressure for the energy estimation */ > > > > cpu = cpumask_first(cpus); > > > > - cpu_thermal_cap = arch_scale_cpu_capacity(cpu); > > > > - cpu_thermal_cap -= arch_scale_thermal_pressure(cpu); > > > > + cpu_actual_cap = get_actual_cpu_capacity(cpu); > > > > > > > > - eenv.cpu_cap = cpu_thermal_cap; > > > > + eenv.cpu_cap = cpu_actual_cap; > > > > eenv.pd_cap = 0; > > > > > > > > for_each_cpu(cpu, cpus) { > > > > struct rq *rq = cpu_rq(cpu); > > > > > > > > - eenv.pd_cap += cpu_thermal_cap; > > > > + eenv.pd_cap += cpu_actual_cap; > > > > > > > > if (!cpumask_test_cpu(cpu, sched_domain_span(sd))) > > > > continue; > > > > @@ -8022,7 +8030,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > > > if (prev_delta < base_energy) > > > > goto unlock; > > > > prev_delta -= base_energy; > > > > - prev_thermal_cap = cpu_thermal_cap; > > > > + prev_actual_cap = cpu_actual_cap; > > > > best_delta = min(best_delta, prev_delta); > > > > } > > > > > > > > @@ -8037,7 +8045,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > > > * but best energy cpu has better capacity. > > > > */ > > > > if ((max_fits < 0) && > > > > - (cpu_thermal_cap <= best_thermal_cap)) > > > > + (cpu_actual_cap <= best_actual_cap)) > > > > continue; > > > > > > > > cur_delta = compute_energy(&eenv, pd, cpus, p, > > > > @@ -8058,14 +8066,14 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > > > best_delta = cur_delta; > > > > best_energy_cpu = max_spare_cap_cpu; > > > > best_fits = max_fits; > > > > - best_thermal_cap = cpu_thermal_cap; > > > > + best_actual_cap = cpu_actual_cap; > > > > } > > > > } > > > > rcu_read_unlock(); > > > > > > > > if ((best_fits > prev_fits) || > > > > ((best_fits > 0) && (best_delta < prev_delta)) || > > > > - ((best_fits < 0) && (best_thermal_cap > prev_thermal_cap))) > > > > + ((best_fits < 0) && (best_actual_cap > prev_actual_cap))) > > > > target = best_energy_cpu; > > > > > > > > return target; > > > > @@ -9441,8 +9449,8 @@ static inline void init_sd_lb_stats(struct sd_lb_stats *sds) > > > > > > > > static unsigned long scale_rt_capacity(int cpu) > > > > { > > > > + unsigned long max = get_actual_cpu_capacity(cpu); > > > > struct rq *rq = cpu_rq(cpu); > > > > - unsigned long max = arch_scale_cpu_capacity(cpu); > > > > unsigned long used, free; > > > > unsigned long irq; > > > > > > > > @@ -9454,12 +9462,9 @@ static unsigned long scale_rt_capacity(int cpu) > > > > /* > > > > * avg_rt.util_avg and avg_dl.util_avg track binary signals > > > > * (running and not running) with weights 0 and 1024 respectively. > > > > - * avg_thermal.load_avg tracks thermal pressure and the weighted > > > > - * average uses the actual delta max capacity(load). > > > > */ > > > > used = READ_ONCE(rq->avg_rt.util_avg); > > > > used += READ_ONCE(rq->avg_dl.util_avg); > > > > - used += thermal_load_avg(rq); > > > > > > > > if (unlikely(used >= max)) > > > > return 1; > > > > -- > > > > 2.34.1 > > > >