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cpufreq: schedutil: Avoid missing updates for one-CPU policies

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Commit 152db033d7 (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 <rafael.j.wysocki@intel.com>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
This commit is contained in:
Rafael J. Wysocki 2018-05-23 11:47:45 +02:00
parent 152db033d7
commit a61dec7447
1 changed files with 47 additions and 23 deletions
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70
kernel/sched/cpufreq_schedutil.c
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@ -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;
}
policy->cur = next_freq;
trace_cpu_frequency(next_freq, smp_processor_id());
} else if (!sg_policy->work_in_progress) {
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());
}
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);