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cpufreq: schedutil: move slow path from workqueue to SCHED_FIFO task

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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>
This commit is contained in:
Viresh Kumar 2016-11-15 13:53:22 +05:30 committed by Rafael J. Wysocki
parent 4a71ce4348
commit 02a7b1ee3b
1 changed files with 78 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

85
kernel/sched/cpufreq_schedutil.c
View File

@ -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, &param);
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 @@ fail:
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)