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cpufreq: Reduce cpufreq_update_util() overhead a bit
Use the observation that cpufreq_update_util() is only called by the scheduler with rq->lock held, so the callers of cpufreq_set_update_util_data() can use synchronize_sched() instead of synchronize_rcu() to wait for cpufreq_update_util() to complete. Moreover, if they are updated to do that, rcu_read_(un)lock() calls in cpufreq_update_util() might be replaced with rcu_read_(un)lock_sched(), respectively, but those aren't really necessary, because the scheduler calls that function from RCU-sched read-side critical sections already. In addition to that, if cpufreq_set_update_util_data() checks the func field in the struct update_util_data before setting the per-CPU pointer to it, the data->func check may be dropped from cpufreq_update_util() as well. Make the above changes to reduce the overhead from cpufreq_update_util() in the scheduler paths invoking it and to make the cleanup after removing its callbacks less heavy-weight somewhat. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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@ -115,12 +115,15 @@ static DEFINE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
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* to call from cpufreq_update_util(). That function will be called from an RCU
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* read-side critical section, so it must not sleep.
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*
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* Callers must use RCU callbacks to free any memory that might be accessed
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* via the old update_util_data pointer or invoke synchronize_rcu() right after
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* this function to avoid use-after-free.
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* Callers must use RCU-sched callbacks to free any memory that might be
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* accessed via the old update_util_data pointer or invoke synchronize_sched()
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* right after this function to avoid use-after-free.
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*/
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void cpufreq_set_update_util_data(int cpu, struct update_util_data *data)
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{
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if (WARN_ON(data && !data->func))
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return;
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rcu_assign_pointer(per_cpu(cpufreq_update_util_data, cpu), data);
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}
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EXPORT_SYMBOL_GPL(cpufreq_set_update_util_data);
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@ -133,18 +136,24 @@ EXPORT_SYMBOL_GPL(cpufreq_set_update_util_data);
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*
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* This function is called by the scheduler on every invocation of
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* update_load_avg() on the CPU whose utilization is being updated.
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*
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* It can only be called from RCU-sched read-side critical sections.
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*/
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void cpufreq_update_util(u64 time, unsigned long util, unsigned long max)
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{
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struct update_util_data *data;
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rcu_read_lock();
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#ifdef CONFIG_LOCKDEP
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WARN_ON(debug_locks && !rcu_read_lock_sched_held());
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#endif
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data = rcu_dereference(*this_cpu_ptr(&cpufreq_update_util_data));
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if (data && data->func)
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data = rcu_dereference_sched(*this_cpu_ptr(&cpufreq_update_util_data));
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/*
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* If this isn't inside of an RCU-sched read-side critical section, data
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* may become NULL after the check below.
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*/
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if (data)
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data->func(data, time, util, max);
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rcu_read_unlock();
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}
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/* Flag to suspend/resume CPUFreq governors */
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@ -280,7 +280,7 @@ static inline void gov_clear_update_util(struct cpufreq_policy *policy)
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for_each_cpu(i, policy->cpus)
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cpufreq_set_update_util_data(i, NULL);
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synchronize_rcu();
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synchronize_sched();
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}
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static void gov_cancel_work(struct cpufreq_policy *policy)
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@ -1168,7 +1168,7 @@ static void intel_pstate_stop_cpu(struct cpufreq_policy *policy)
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pr_debug("intel_pstate: CPU %d exiting\n", cpu_num);
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cpufreq_set_update_util_data(cpu_num, NULL);
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synchronize_rcu();
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synchronize_sched();
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if (hwp_active)
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return;
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@ -1426,7 +1426,7 @@ out:
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for_each_online_cpu(cpu) {
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if (all_cpu_data[cpu]) {
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cpufreq_set_update_util_data(cpu, NULL);
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synchronize_rcu();
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synchronize_sched();
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kfree(all_cpu_data[cpu]);
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}
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}
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