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From 389b1838b500ecc431c2421ee399b8f737e88cf5 Mon Sep 17 00:00:00 2001
From: Viresh Kumar <viresh.kumar@linaro.org>
Date: Tue, 15 Nov 2016 13:53:22 +0530
Subject: [PATCH 18/92] cpufreq: schedutil: move slow path from workqueue to
SCHED_FIFO task
If slow path frequency changes are conducted in a SCHED_OTHER context
then they may be delayed for some amount of time, including
indefinitely, when real time or deadline activity is taking place.
Move the slow path to a real time kernel thread. In the future the
thread should be made SCHED_DEADLINE. The RT priority is arbitrarily set
to 50 for now.
Hackbench results on ARM Exynos, dual core A15 platform for 10
iterations:
$ hackbench -s 100 -l 100 -g 10 -f 20
Before After
---------------------------------
1.808 1.603
1.847 1.251
2.229 1.590
1.952 1.600
1.947 1.257
1.925 1.627
2.694 1.620
1.258 1.621
1.919 1.632
1.250 1.240
Average:
1.8829 1.5041
Based on initial work by Steve Muckle.
Signed-off-by: Steve Muckle <smuckle.linux@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit 02a7b1ee3baa15a98b541d8cfd156bbe1a091c20)
Signed-off-by: Gaku Inami <gaku.inami.xw@bp.renesas.com>
---
kernel/sched/cpufreq_schedutil.c | 85 ++++++++++++++++++++++++++++++++++++----
1 file changed, 78 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 68f21bb..f165ba0 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -12,11 +12,14 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/cpufreq.h>
+#include <linux/kthread.h>
#include <linux/slab.h>
#include <trace/events/power.h>
#include "sched.h"
+#define SUGOV_KTHREAD_PRIORITY 50
+
struct sugov_tunables {
struct gov_attr_set attr_set;
unsigned int rate_limit_us;
@@ -35,8 +38,10 @@ struct sugov_policy {
/* The next fields are only needed if fast switch cannot be used. */
struct irq_work irq_work;
- struct work_struct work;
+ struct kthread_work work;
struct mutex work_lock;
+ struct kthread_worker worker;
+ struct task_struct *thread;
bool work_in_progress;
bool need_freq_update;
@@ -291,7 +296,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
raw_spin_unlock(&sg_policy->update_lock);
}
-static void sugov_work(struct work_struct *work)
+static void sugov_work(struct kthread_work *work)
{
struct sugov_policy *sg_policy = container_of(work, struct sugov_policy, work);
@@ -308,7 +313,21 @@ static void sugov_irq_work(struct irq_work *irq_work)
struct sugov_policy *sg_policy;
sg_policy = container_of(irq_work, struct sugov_policy, irq_work);
- schedule_work_on(smp_processor_id(), &sg_policy->work);
+
+ /*
+ * For Real Time and Deadline tasks, schedutil governor shoots the
+ * frequency to maximum. And special care must be taken to ensure that
+ * this kthread doesn't result in that.
+ *
+ * This is (mostly) guaranteed by the work_in_progress flag. The flag is
+ * updated only at the end of the sugov_work() and before that schedutil
+ * rejects all other frequency scaling requests.
+ *
+ * Though there is a very rare case where the RT thread yields right
+ * after the work_in_progress flag is cleared. The effects of that are
+ * neglected for now.
+ */
+ kthread_queue_work(&sg_policy->worker, &sg_policy->work);
}
/************************** sysfs interface ************************/
@@ -372,7 +391,6 @@ static struct sugov_policy *sugov_policy_alloc(struct cpufreq_policy *policy)
sg_policy->policy = policy;
init_irq_work(&sg_policy->irq_work, sugov_irq_work);
- INIT_WORK(&sg_policy->work, sugov_work);
mutex_init(&sg_policy->work_lock);
raw_spin_lock_init(&sg_policy->update_lock);
return sg_policy;
@@ -384,6 +402,51 @@ static void sugov_policy_free(struct sugov_policy *sg_policy)
kfree(sg_policy);
}
+static int sugov_kthread_create(struct sugov_policy *sg_policy)
+{
+ struct task_struct *thread;
+ struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO / 2 };
+ struct cpufreq_policy *policy = sg_policy->policy;
+ int ret;
+
+ /* kthread only required for slow path */
+ if (policy->fast_switch_enabled)
+ return 0;
+
+ kthread_init_work(&sg_policy->work, sugov_work);
+ kthread_init_worker(&sg_policy->worker);
+ thread = kthread_create(kthread_worker_fn, &sg_policy->worker,
+ "sugov:%d",
+ cpumask_first(policy->related_cpus));
+ if (IS_ERR(thread)) {
+ pr_err("failed to create sugov thread: %ld\n", PTR_ERR(thread));
+ return PTR_ERR(thread);
+ }
+
+ ret = sched_setscheduler_nocheck(thread, SCHED_FIFO, ¶m);
+ if (ret) {
+ kthread_stop(thread);
+ pr_warn("%s: failed to set SCHED_FIFO\n", __func__);
+ return ret;
+ }
+
+ sg_policy->thread = thread;
+ kthread_bind_mask(thread, policy->related_cpus);
+ wake_up_process(thread);
+
+ return 0;
+}
+
+static void sugov_kthread_stop(struct sugov_policy *sg_policy)
+{
+ /* kthread only required for slow path */
+ if (sg_policy->policy->fast_switch_enabled)
+ return;
+
+ kthread_flush_worker(&sg_policy->worker);
+ kthread_stop(sg_policy->thread);
+}
+
static struct sugov_tunables *sugov_tunables_alloc(struct sugov_policy *sg_policy)
{
struct sugov_tunables *tunables;
@@ -424,12 +487,16 @@ static int sugov_init(struct cpufreq_policy *policy)
goto disable_fast_switch;
}
+ ret = sugov_kthread_create(sg_policy);
+ if (ret)
+ goto free_sg_policy;
+
mutex_lock(&global_tunables_lock);
if (global_tunables) {
if (WARN_ON(have_governor_per_policy())) {
ret = -EINVAL;
- goto free_sg_policy;
+ goto stop_kthread;
}
policy->governor_data = sg_policy;
sg_policy->tunables = global_tunables;
@@ -441,7 +508,7 @@ static int sugov_init(struct cpufreq_policy *policy)
tunables = sugov_tunables_alloc(sg_policy);
if (!tunables) {
ret = -ENOMEM;
- goto free_sg_policy;
+ goto stop_kthread;
}
tunables->rate_limit_us = LATENCY_MULTIPLIER;
@@ -466,6 +533,9 @@ static int sugov_init(struct cpufreq_policy *policy)
policy->governor_data = NULL;
sugov_tunables_free(tunables);
+stop_kthread:
+ sugov_kthread_stop(sg_policy);
+
free_sg_policy:
mutex_unlock(&global_tunables_lock);
@@ -493,6 +563,7 @@ static void sugov_exit(struct cpufreq_policy *policy)
mutex_unlock(&global_tunables_lock);
+ sugov_kthread_stop(sg_policy);
sugov_policy_free(sg_policy);
cpufreq_disable_fast_switch(policy);
}
@@ -541,7 +612,7 @@ static void sugov_stop(struct cpufreq_policy *policy)
synchronize_sched();
irq_work_sync(&sg_policy->irq_work);
- cancel_work_sync(&sg_policy->work);
+ kthread_cancel_work_sync(&sg_policy->work);
}
static void sugov_limits(struct cpufreq_policy *policy)
--
1.9.1
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