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Subject[PATCH] cpufreq: schedutil: Avoid missing updates for one-CPU policies
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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 <rafael.j.wysocki@intel.com>
---
kernel/sched/cpufreq_schedutil.c | 70 ++++++++++++++++++++++++++-------------
1 file changed, 47 insertions(+), 23 deletions(-)

Index: linux-pm/kernel/sched/cpufreq_schedutil.c
===================================================================
--- linux-pm.orig/kernel/sched/cpufreq_schedutil.c
+++ linux-pm/kernel/sched/cpufreq_schedutil.c
@@ -100,25 +100,41 @@ static bool sugov_should_update_freq(str
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 u

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 u
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_d

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_wo
/*
* 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);
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