From a61dec7447456858dfc88fe056017a91ab903ed0 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Wed, 23 May 2018 11:47:45 +0200 Subject: [PATCH] cpufreq: schedutil: Avoid missing updates for one-CPU policies Commit 152db033d775 (schedutil: Allow cpufreq requests to be made even when kthread kicked) made changes to prevent utilization updates from being discarded during processing a previous request, but it left a small window in which that still can happen in the one-CPU policy case. Namely, updates coming in after setting work_in_progress in sugov_update_commit() and clearing it in sugov_work() will still be dropped due to the work_in_progress check in sugov_update_single(). To close that window, rearrange the code so as to acquire the update lock around the deferred update branch in sugov_update_single() and drop the work_in_progress check from it. Signed-off-by: Rafael J. Wysocki Reviewed-by: Juri Lelli Acked-by: Viresh Kumar Reviewed-by: Joel Fernandes (Google) --- kernel/sched/cpufreq_schedutil.c | 70 +++++++++++++++++++++----------- 1 file changed, 47 insertions(+), 23 deletions(-) diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index 178946e36393..fd76497efeb1 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -100,25 +100,41 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time) return delta_ns >= sg_policy->freq_update_delay_ns; } -static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time, - unsigned int next_freq) +static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time, + unsigned int next_freq) { - struct cpufreq_policy *policy = sg_policy->policy; - if (sg_policy->next_freq == next_freq) - return; + return false; sg_policy->next_freq = next_freq; sg_policy->last_freq_update_time = time; - if (policy->fast_switch_enabled) { - next_freq = cpufreq_driver_fast_switch(policy, next_freq); - if (!next_freq) - return; + return true; +} + +static void sugov_fast_switch(struct sugov_policy *sg_policy, u64 time, + unsigned int next_freq) +{ + struct cpufreq_policy *policy = sg_policy->policy; + + if (!sugov_update_next_freq(sg_policy, time, next_freq)) + return; + + next_freq = cpufreq_driver_fast_switch(policy, next_freq); + if (!next_freq) + return; - policy->cur = next_freq; - trace_cpu_frequency(next_freq, smp_processor_id()); - } else if (!sg_policy->work_in_progress) { + policy->cur = next_freq; + trace_cpu_frequency(next_freq, smp_processor_id()); +} + +static void sugov_deferred_update(struct sugov_policy *sg_policy, u64 time, + unsigned int next_freq) +{ + if (!sugov_update_next_freq(sg_policy, time, next_freq)) + return; + + if (!sg_policy->work_in_progress) { sg_policy->work_in_progress = true; irq_work_queue(&sg_policy->irq_work); } @@ -363,13 +379,6 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, ignore_dl_rate_limit(sg_cpu, sg_policy); - /* - * For slow-switch systems, single policy requests can't run at the - * moment if update is in progress, unless we acquire update_lock. - */ - if (sg_policy->work_in_progress) - return; - if (!sugov_should_update_freq(sg_policy, time)) return; @@ -391,7 +400,18 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, sg_policy->cached_raw_freq = 0; } - sugov_update_commit(sg_policy, time, next_f); + /* + * This code runs under rq->lock for the target CPU, so it won't run + * concurrently on two different CPUs for the same target and it is not + * necessary to acquire the lock in the fast switch case. + */ + if (sg_policy->policy->fast_switch_enabled) { + sugov_fast_switch(sg_policy, time, next_f); + } else { + raw_spin_lock(&sg_policy->update_lock); + sugov_deferred_update(sg_policy, time, next_f); + raw_spin_unlock(&sg_policy->update_lock); + } } static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) @@ -435,7 +455,11 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags) if (sugov_should_update_freq(sg_policy, time)) { next_f = sugov_next_freq_shared(sg_cpu, time); - sugov_update_commit(sg_policy, time, next_f); + + if (sg_policy->policy->fast_switch_enabled) + sugov_fast_switch(sg_policy, time, next_f); + else + sugov_deferred_update(sg_policy, time, next_f); } raw_spin_unlock(&sg_policy->update_lock); @@ -450,11 +474,11 @@ static void sugov_work(struct kthread_work *work) /* * Hold sg_policy->update_lock shortly to handle the case where: * incase sg_policy->next_freq is read here, and then updated by - * sugov_update_shared just before work_in_progress is set to false + * sugov_deferred_update() just before work_in_progress is set to false * here, we may miss queueing the new update. * * Note: If a work was queued after the update_lock is released, - * sugov_work will just be called again by kthread_work code; and the + * sugov_work() will just be called again by kthread_work code; and the * request will be proceed before the sugov thread sleeps. */ raw_spin_lock_irqsave(&sg_policy->update_lock, flags); -- 2.30.2