Messages in this thread | | | Date | Tue, 8 May 2018 12:24:35 +0530 | From | Viresh Kumar <> | Subject | Re: [RFC PATCH] sched/cpufreq/schedutil: handling urgent frequency requests |
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On 07-05-18, 16:43, Claudio Scordino wrote: > At OSPM, it was mentioned the issue about urgent CPU frequency requests > arriving when a frequency switch is already in progress. > > Besides the various issues (physical time for switching frequency, > on-going kthread activity, etc.) one (minor) issue is the kernel > "forgetting" such request, thus waiting the next switch time for > recomputing the needed frequency and behaving accordingly. > > This patch makes the kthread serve any urgent request occurred during > the previous frequency switch. It introduces a specific flag, only set > when the SCHED_DEADLINE scheduling class increases the CPU utilization, > aiming at decreasing the likelihood of a deadline miss. > > Indeed, some preliminary tests in critical conditions (i.e. > SCHED_DEADLINE tasks with short periods) have shown reductions of more > than 10% of the average number of deadline misses. On the other hand, > the increase in terms of energy consumption when running SCHED_DEADLINE > tasks (not yet measured) is likely to be not negligible (especially in > case of critical scenarios like "ramp up" utilizations). > > The patch is meant as follow-up discussion after OSPM. > > Signed-off-by: Claudio Scordino <claudio@evidence.eu.com> > CC: Viresh Kumar <viresh.kumar@linaro.org> > CC: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > CC: Peter Zijlstra <peterz@infradead.org> > CC: Ingo Molnar <mingo@redhat.com> > CC: Patrick Bellasi <patrick.bellasi@arm.com> > CC: Juri Lelli <juri.lelli@redhat.com> > Cc: Luca Abeni <luca.abeni@santannapisa.it> > CC: Joel Fernandes <joelaf@google.com> > CC: linux-pm@vger.kernel.org > --- > kernel/sched/cpufreq_schedutil.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > index d2c6083..4de06b0 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -41,6 +41,7 @@ struct sugov_policy { > bool work_in_progress; > > bool need_freq_update; > + bool urgent_freq_update; > }; > > struct sugov_cpu { > @@ -92,6 +93,14 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time) > !cpufreq_can_do_remote_dvfs(sg_policy->policy)) > return false; > > + /* > + * Continue computing the new frequency. In case of work_in_progress, > + * the kthread will resched a change once the current transition is > + * finished. > + */ > + if (sg_policy->urgent_freq_update) > + return true; > + > if (sg_policy->work_in_progress) > return false; > > @@ -121,6 +130,9 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time, > sg_policy->next_freq = next_freq; > sg_policy->last_freq_update_time = time; > > + if (sg_policy->work_in_progress) > + return; > + > if (policy->fast_switch_enabled) { > next_freq = cpufreq_driver_fast_switch(policy, next_freq); > if (!next_freq) > @@ -274,7 +286,7 @@ static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; } > static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu, struct sugov_policy *sg_policy) > { > if (cpu_util_dl(cpu_rq(sg_cpu->cpu)) > sg_cpu->util_dl) > - sg_policy->need_freq_update = true; > + sg_policy->urgent_freq_update = true; > } > > static void sugov_update_single(struct update_util_data *hook, u64 time, > @@ -383,8 +395,11 @@ static void sugov_work(struct kthread_work *work) > struct sugov_policy *sg_policy = container_of(work, struct sugov_policy, work); > > mutex_lock(&sg_policy->work_lock); > - __cpufreq_driver_target(sg_policy->policy, sg_policy->next_freq, > + do { > + sg_policy->urgent_freq_update = false; > + __cpufreq_driver_target(sg_policy->policy, sg_policy->next_freq, > CPUFREQ_RELATION_L);
If we are going to solve this problem, then maybe instead of the added complexity and a new flag we can look for need_freq_update flag at this location and re-calculate the next frequency if required.
> + } while (sg_policy->urgent_freq_update); > mutex_unlock(&sg_policy->work_lock); > > sg_policy->work_in_progress = false; > @@ -673,6 +688,7 @@ static int sugov_start(struct cpufreq_policy *policy) > sg_policy->next_freq = UINT_MAX; > sg_policy->work_in_progress = false; > sg_policy->need_freq_update = false; > + sg_policy->urgent_freq_update = false; > sg_policy->cached_raw_freq = 0; > > for_each_cpu(cpu, policy->cpus) { > -- > 2.7.4
-- viresh
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