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 --- kernel/sched/cpufreq_schedutil.c | 62 ++++++++++++++++++++++++++++++++-------- 1 file changed, 50 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index ccb2ab89affb..045ce0a4e6d1 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -12,6 +12,7 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/cpufreq.h> +#include <linux/kthread.h> #include <linux/slab.h> #include <trace/events/power.h>
@@ -35,8 +36,10 @@ 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; @@ -291,9 +294,10 @@ 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); + struct sugov_policy *sg_policy = + container_of(work, struct sugov_policy, work);
mutex_lock(&sg_policy->work_lock); __cpufreq_driver_target(sg_policy->policy, sg_policy->next_freq, @@ -308,7 +312,7 @@ 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); + kthread_queue_work(&sg_policy->worker, &sg_policy->work); }
/************************** sysfs interface ************************/ @@ -362,9 +366,23 @@ static struct kobj_type sugov_tunables_ktype = {
static struct cpufreq_governor schedutil_gov;
+static void sugov_policy_free(struct sugov_policy *sg_policy) +{ + if (!sg_policy->policy->fast_switch_enabled) { + kthread_flush_worker(&sg_policy->worker); + kthread_stop(sg_policy->thread); + } + + mutex_destroy(&sg_policy->work_lock); + kfree(sg_policy); +} + static struct sugov_policy *sugov_policy_alloc(struct cpufreq_policy *policy) { struct sugov_policy *sg_policy; + struct task_struct *thread; + struct sched_param param = { .sched_priority = 50 }; + int ret;
sg_policy = kzalloc(sizeof(*sg_policy), GFP_KERNEL); if (!sg_policy) @@ -372,16 +390,36 @@ 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; -}
-static void sugov_policy_free(struct sugov_policy *sg_policy) -{ - mutex_destroy(&sg_policy->work_lock); - kfree(sg_policy); + /* kthread only required for slow path */ + if (policy->fast_switch_enabled) + return sg_policy; + + 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)) { + mutex_destroy(&sg_policy->work_lock); + kfree(sg_policy); + pr_err("failed to create sugov thread: %ld\n", PTR_ERR(thread)); + return NULL; + } + sg_policy->thread = thread; + + ret = sched_setscheduler_nocheck(thread, SCHED_FIFO, ¶m); + if (ret) { + sugov_policy_free(sg_policy); + pr_warn("%s: failed to set SCHED_FIFO\n", __func__); + return NULL; + } + + kthread_bind_mask(thread, policy->related_cpus); + wake_up_process(thread); + + return sg_policy; }
static struct sugov_tunables *sugov_tunables_alloc(struct sugov_policy *sg_policy) @@ -541,7 +579,7 @@ 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)