2020-01-21 06:34:24

by Parth Shah

Subject: [RFC v6 1/5] sched: Introduce switch to enable TurboSched for task packing

Create a static key which allows to enable or disable TurboSched feature at
runtime.

This key is added in order to enable the TurboSched feature only when
required. This helps in optimizing the scheduler fast-path when the
TurboSched feature is disabled.

Also provide get/put methods to keep track of the tasks using the
TurboSched feature and also refcount classified background tasks. This
allows to enable the feature on setting first task classified as background
noise, similarly disable the feature on unsetting of such last task.

Signed-off-by: Parth Shah <[email protected]>
---
kernel/sched/core.c | 25 +++++++++++++++++++++++++
kernel/sched/sched.h | 12 ++++++++++++
2 files changed, 37 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a9e5d157b1a5..dfbb52d66b29 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -73,6 +73,31 @@ __read_mostly int scheduler_running;
*/
int sysctl_sched_rt_runtime = 950000;

+#ifdef CONFIG_SCHED_SMT
+DEFINE_STATIC_KEY_FALSE(__turbo_sched_enabled);
+static DEFINE_MUTEX(turbo_sched_lock);
+static int turbo_sched_count;
+
+void turbo_sched_get(void)
+{
+ mutex_lock(&turbo_sched_lock);
+ if (!turbo_sched_count++)
+ static_branch_enable(&__turbo_sched_enabled);
+ mutex_unlock(&turbo_sched_lock);
+}
+
+void turbo_sched_put(void)
+{
+ mutex_lock(&turbo_sched_lock);
+ if (!--turbo_sched_count)
+ static_branch_disable(&__turbo_sched_enabled);
+ mutex_unlock(&turbo_sched_lock);
+}
+#else
+void turbo_sched_get(void) { return ; }
+void turbo_sched_get(void) { return ; }
+#endif
+
/*
* __task_rq_lock - lock the rq @p resides on.
*/
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index edae9277e48d..f841297b7d56 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2497,3 +2497,15 @@ static inline void membarrier_switch_mm(struct rq *rq,
{
}
#endif
+
+void turbo_sched_get(void);
+void turbo_sched_put(void);
+
+#ifdef CONFIG_SCHED_SMT
+DECLARE_STATIC_KEY_FALSE(__turbo_sched_enabled);
+
+static inline bool is_turbosched_enabled(void)
+{
+ return static_branch_unlikely(&__turbo_sched_enabled);
+}
+#endif
--
2.17.2

2020-01-22 21:39:21

by Tim Chen

Subject: Re: [RFC v6 1/5] sched: Introduce switch to enable TurboSched for task packing

On 1/20/20 10:33 PM, Parth Shah wrote:
> Create a static key which allows to enable or disable TurboSched feature at
> runtime.
>
> This key is added in order to enable the TurboSched feature only when
> required. This helps in optimizing the scheduler fast-path when the
> TurboSched feature is disabled.
>
> Also provide get/put methods to keep track of the tasks using the
> TurboSched feature and also refcount classified background tasks. This
> allows to enable the feature on setting first task classified as background
> noise, similarly disable the feature on unsetting of such last task.
>
> Signed-off-by: Parth Shah <[email protected]>
> ---
> kernel/sched/core.c | 25 +++++++++++++++++++++++++
> kernel/sched/sched.h | 12 ++++++++++++
> 2 files changed, 37 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a9e5d157b1a5..dfbb52d66b29 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -73,6 +73,31 @@ __read_mostly int scheduler_running;
> */
> int sysctl_sched_rt_runtime = 950000;
>
> +#ifdef CONFIG_SCHED_SMT
> +DEFINE_STATIC_KEY_FALSE(__turbo_sched_enabled);
> +static DEFINE_MUTEX(turbo_sched_lock);
> +static int turbo_sched_count;
> +
> +void turbo_sched_get(void)
> +{
> + mutex_lock(&turbo_sched_lock);
> + if (!turbo_sched_count++)
> + static_branch_enable(&__turbo_sched_enabled);

If you use static_branch_inc(&__turbo_sched_enabled) and
static_branch_dec(&__turbo_sched_enabled), you don't have
to define turbo_sched_count. And turbo_sched_lock is
also unnecessary as static_branch_inc/dec are atomic.

> + mutex_unlock(&turbo_sched_lock);
> +}
> +
> +void turbo_sched_put(void)
> +{
> + mutex_lock(&turbo_sched_lock);
> + if (!--turbo_sched_count)
> + static_branch_disable(&__turbo_sched_enabled);
> + mutex_unlock(&turbo_sched_lock);
> +}
> +#else
> +void turbo_sched_get(void) { return ; }
> +void turbo_sched_get(void) { return ; }

Double definition of turbo_sched_get.
You probably meant turbo_sched_put in the second definition.

Tim

2020-01-23 06:37:24

by Parth Shah

Subject: Re: [RFC v6 1/5] sched: Introduce switch to enable TurboSched for task packing

On 1/23/20 3:07 AM, Tim Chen wrote:
> On 1/20/20 10:33 PM, Parth Shah wrote:
>> Create a static key which allows to enable or disable TurboSched feature at
>> runtime.
>>
>> This key is added in order to enable the TurboSched feature only when
>> required. This helps in optimizing the scheduler fast-path when the
>> TurboSched feature is disabled.
>>
>> Also provide get/put methods to keep track of the tasks using the
>> TurboSched feature and also refcount classified background tasks. This
>> allows to enable the feature on setting first task classified as background
>> noise, similarly disable the feature on unsetting of such last task.
>>
>> Signed-off-by: Parth Shah <[email protected]>
>> ---
>> kernel/sched/core.c | 25 +++++++++++++++++++++++++
>> kernel/sched/sched.h | 12 ++++++++++++
>> 2 files changed, 37 insertions(+)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index a9e5d157b1a5..dfbb52d66b29 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -73,6 +73,31 @@ __read_mostly int scheduler_running;
>> */
>> int sysctl_sched_rt_runtime = 950000;
>>
>> +#ifdef CONFIG_SCHED_SMT
>> +DEFINE_STATIC_KEY_FALSE(__turbo_sched_enabled);
>> +static DEFINE_MUTEX(turbo_sched_lock);
>> +static int turbo_sched_count;
>> +
>> +void turbo_sched_get(void)
>> +{
>> + mutex_lock(&turbo_sched_lock);
>> + if (!turbo_sched_count++)
>> + static_branch_enable(&__turbo_sched_enabled);
>
> If you use static_branch_inc(&__turbo_sched_enabled) and
> static_branch_dec(&__turbo_sched_enabled), you don't have
> to define turbo_sched_count. And turbo_sched_lock is
> also unnecessary as static_branch_inc/dec are atomic.
>

That's a good suggestion. I will make those changes in the next version.

>> + mutex_unlock(&turbo_sched_lock);
>> +}
>> +
>> +void turbo_sched_put(void)
>> +{
>> + mutex_lock(&turbo_sched_lock);
>> + if (!--turbo_sched_count)
>> + static_branch_disable(&__turbo_sched_enabled);
>> + mutex_unlock(&turbo_sched_lock);
>> +}
>> +#else
>> +void turbo_sched_get(void) { return ; }
>> +void turbo_sched_get(void) { return ; }
>
> Double definition of turbo_sched_get.
> You probably meant turbo_sched_put in the second definition.

yes, my bad. I meant turbo_sched_put() instead.


Thanks,
Parth

>
> Tim
>