[PATCH V2 1/2] sched: Factor out nr_iowait and nr_iowait_cpu

[PATCH V2 1/2] sched: Factor out nr_iowait and nr_iowait_cpu

[Daniel Lezcano]

The function nr_iowait_cpu() can be used directly by nr_iowait() instead
of duplicating code.

Call nr_iowait_cpu() from nr_iowait()

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
 kernel/sched/core.c | 41 ++++++++++++++++++++---------------------
 1 file changed, 20 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 625bc98..43efb74 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2875,6 +2875,25 @@ unsigned long long nr_context_switches(void)
 }
 
 /*
+ * Consumers of these two interfaces, like for example the cpufreq menu
+ * governor are using nonsensical data. Boosting frequency for a CPU that has
+ * IO-wait which might not even end up running the task when it does become
+ * runnable.
+ */
+
+unsigned long nr_iowait_cpu(int cpu)
+{
+	return atomic_read(&cpu_rq(cpu)->nr_iowait);
+}
+
+void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
+{
+	struct rq *rq = this_rq();
+	*nr_waiters = atomic_read(&rq->nr_iowait);
+	*load = rq->load.weight;
+}
+
+/*
  * IO-wait accounting, and how its mostly bollocks (on SMP).
  *
  * The idea behind IO-wait account is to account the idle time that we could
@@ -2909,31 +2928,11 @@ unsigned long nr_iowait(void)
 	unsigned long i, sum = 0;
 
 	for_each_possible_cpu(i)
-		sum += atomic_read(&cpu_rq(i)->nr_iowait);
+		sum += nr_iowait_cpu(i);
 
 	return sum;
 }
 
-/*
- * Consumers of these two interfaces, like for example the cpufreq menu
- * governor are using nonsensical data. Boosting frequency for a CPU that has
- * IO-wait which might not even end up running the task when it does become
- * runnable.
- */
-
-unsigned long nr_iowait_cpu(int cpu)
-{
-	struct rq *this = cpu_rq(cpu);
-	return atomic_read(&this->nr_iowait);
-}
-
-void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
-{
-	struct rq *rq = this_rq();
-	*nr_waiters = atomic_read(&rq->nr_iowait);
-	*load = rq->load.weight;
-}
-
 #ifdef CONFIG_SMP
 
 /*
-- 
2.7.4

[PATCH V2 2/2] cpuidle/drivers/menu: Remove get_loadavg in the performance multiplier

[Daniel Lezcano]

The function get_loadavg() returns almost always zero. To be more
precise, statistically speaking for a total of 1023379 times passing
in the function, the load is equal to zero 1020728 times, greater than
100, 610 times, the remaining is between 0 and 5.

In 2011, the get_loadavg() was removed from the Android tree because
of the above [1]. At this time, the load was:

unsigned long this_cpu_load(void)
{
        struct rq *this = this_rq();
        return this->cpu_load[0];
}

In 2014, the code was changed by commit 372ba8cb46b2 (cpuidle: menu: Lookup CPU
runqueues less) and the load is:

void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
{
        struct rq *rq = this_rq();
        *nr_waiters = atomic_read(&rq->nr_iowait);
        *load = rq->load.weight;
}

with the same result.

Both measurements show using the load in this code path does no matter
anymore. Removing it.

[1] https://android.googlesource.com/kernel/common/+/4dedd9f124703207895777ac6e91dacde0f7cc17

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Todd Kjos <tkjos@google.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Colin Cross <ccross@android.com>
Cc: Ramesh Thomas <ramesh.thomas@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
 drivers/cpuidle/governors/menu.c | 26 +++++++-------------------
 include/linux/sched/stat.h       |  1 -
 kernel/sched/core.c              |  7 -------
 3 files changed, 7 insertions(+), 27 deletions(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index e26a409..066b01f 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -135,11 +135,6 @@ struct menu_device {
 #define LOAD_INT(x) ((x) >> FSHIFT)
 #define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
 
-static inline int get_loadavg(unsigned long load)
-{
-	return LOAD_INT(load) * 10 + LOAD_FRAC(load) / 10;
-}
-
 static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters)
 {
 	int bucket = 0;
@@ -173,18 +168,10 @@ static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters
  * to be, the higher this multiplier, and thus the higher
  * the barrier to go to an expensive C state.
  */
-static inline int performance_multiplier(unsigned long nr_iowaiters, unsigned long load)
+static inline int performance_multiplier(unsigned long nr_iowaiters)
 {
-	int mult = 1;
-
-	/* for higher loadavg, we are more reluctant */
-
-	mult += 2 * get_loadavg(load);
-
-	/* for IO wait tasks (per cpu!) we add 5x each */
-	mult += 10 * nr_iowaiters;
-
-	return mult;
+	/* for IO wait tasks (per cpu!) we add 10x each */
+	return 1 + 10 * nr_iowaiters;
 }
 
 static DEFINE_PER_CPU(struct menu_device, menu_devices);
@@ -290,7 +277,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 	int idx;
 	unsigned int interactivity_req;
 	unsigned int expected_interval;
-	unsigned long nr_iowaiters, cpu_load;
+	unsigned long nr_iowaiters;
 	ktime_t delta_next;
 
 	if (data->needs_update) {
@@ -307,7 +294,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 	/* determine the expected residency time, round up */
 	data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length(&delta_next));
 
-	get_iowait_load(&nr_iowaiters, &cpu_load);
+	nr_iowaiters = nr_iowait_cpu(dev->cpu);
 	data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);
 
 	/*
@@ -359,7 +346,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 		 * Use the performance multiplier and the user-configurable
 		 * latency_req to determine the maximum exit latency.
 		 */
-		interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
+		interactivity_req = data->predicted_us /
+			performance_multiplier(nr_iowaiters);
 		if (latency_req > interactivity_req)
 			latency_req = interactivity_req;
 	}
diff --git a/include/linux/sched/stat.h b/include/linux/sched/stat.h
index 04f1321..f30954c 100644
--- a/include/linux/sched/stat.h
+++ b/include/linux/sched/stat.h
@@ -20,7 +20,6 @@ extern unsigned long nr_running(void);
 extern bool single_task_running(void);
 extern unsigned long nr_iowait(void);
 extern unsigned long nr_iowait_cpu(int cpu);
-extern void get_iowait_load(unsigned long *nr_waiters, unsigned long *load);
 
 static inline int sched_info_on(void)
 {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 43efb74..48a786a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2886,13 +2886,6 @@ unsigned long nr_iowait_cpu(int cpu)
 	return atomic_read(&cpu_rq(cpu)->nr_iowait);
 }
 
-void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
-{
-	struct rq *rq = this_rq();
-	*nr_waiters = atomic_read(&rq->nr_iowait);
-	*load = rq->load.weight;
-}
-
 /*
  * IO-wait accounting, and how its mostly bollocks (on SMP).
  *
-- 
2.7.4

Re: [PATCH V2 2/2] cpuidle/drivers/menu: Remove get_loadavg in the performance multiplier

[Mel Gorman]

On Thu, Oct 04, 2018 at 02:04:03PM +0200, Daniel Lezcano wrote:
> The function get_loadavg() returns almost always zero. To be more
> precise, statistically speaking for a total of 1023379 times passing
> in the function, the load is equal to zero 1020728 times, greater than
> 100, 610 times, the remaining is between 0 and 5.
> 
> In 2011, the get_loadavg() was removed from the Android tree because
> of the above [1]. At this time, the load was:
> 
> unsigned long this_cpu_load(void)
> {
>         struct rq *this = this_rq();
>         return this->cpu_load[0];
> }
> 
> In 2014, the code was changed by commit 372ba8cb46b2 (cpuidle: menu: Lookup CPU
> runqueues less) and the load is:
> 
> void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
> {
>         struct rq *rq = this_rq();
>         *nr_waiters = atomic_read(&rq->nr_iowait);
>         *load = rq->load.weight;
> }
> 
> with the same result.
> 
> Both measurements show using the load in this code path does no matter
> anymore. Removing it.
> 
> [1] https://android.googlesource.com/kernel/common/+/4dedd9f124703207895777ac6e91dacde0f7cc17
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Ramesh Thomas <ramesh.thomas@intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

I agree that removing this is the most sensible option so;

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

Re: [PATCH V2 2/2] cpuidle/drivers/menu: Remove get_loadavg in the performance multiplier

[Rafael J. Wysocki]

On Thu, Oct 4, 2018 at 2:04 PM Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>
> The function get_loadavg() returns almost always zero. To be more
> precise, statistically speaking for a total of 1023379 times passing
> in the function, the load is equal to zero 1020728 times, greater than
> 100, 610 times, the remaining is between 0 and 5.
>
> In 2011, the get_loadavg() was removed from the Android tree because
> of the above [1]. At this time, the load was:
>
> unsigned long this_cpu_load(void)
> {
>         struct rq *this = this_rq();
>         return this->cpu_load[0];
> }
>
> In 2014, the code was changed by commit 372ba8cb46b2 (cpuidle: menu: Lookup CPU
> runqueues less) and the load is:
>
> void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
> {
>         struct rq *rq = this_rq();
>         *nr_waiters = atomic_read(&rq->nr_iowait);
>         *load = rq->load.weight;
> }
>
> with the same result.
>
> Both measurements show using the load in this code path does no matter
> anymore. Removing it.
>
> [1] https://android.googlesource.com/kernel/common/+/4dedd9f124703207895777ac6e91dacde0f7cc17
>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Ramesh Thomas <ramesh.thomas@intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
>  drivers/cpuidle/governors/menu.c | 26 +++++++-------------------
>  include/linux/sched/stat.h       |  1 -
>  kernel/sched/core.c              |  7 -------
>  3 files changed, 7 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
> index e26a409..066b01f 100644
> --- a/drivers/cpuidle/governors/menu.c
> +++ b/drivers/cpuidle/governors/menu.c
> @@ -135,11 +135,6 @@ struct menu_device {
>  #define LOAD_INT(x) ((x) >> FSHIFT)
>  #define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
>
> -static inline int get_loadavg(unsigned long load)
> -{
> -       return LOAD_INT(load) * 10 + LOAD_FRAC(load) / 10;
> -}
> -
>  static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters)
>  {
>         int bucket = 0;
> @@ -173,18 +168,10 @@ static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters
>   * to be, the higher this multiplier, and thus the higher
>   * the barrier to go to an expensive C state.
>   */
> -static inline int performance_multiplier(unsigned long nr_iowaiters, unsigned long load)
> +static inline int performance_multiplier(unsigned long nr_iowaiters)
>  {
> -       int mult = 1;
> -
> -       /* for higher loadavg, we are more reluctant */
> -
> -       mult += 2 * get_loadavg(load);
> -
> -       /* for IO wait tasks (per cpu!) we add 5x each */
> -       mult += 10 * nr_iowaiters;
> -
> -       return mult;
> +       /* for IO wait tasks (per cpu!) we add 10x each */
> +       return 1 + 10 * nr_iowaiters;
>  }
>
>  static DEFINE_PER_CPU(struct menu_device, menu_devices);
> @@ -290,7 +277,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>         int idx;
>         unsigned int interactivity_req;
>         unsigned int expected_interval;
> -       unsigned long nr_iowaiters, cpu_load;
> +       unsigned long nr_iowaiters;
>         ktime_t delta_next;
>
>         if (data->needs_update) {
> @@ -307,7 +294,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>         /* determine the expected residency time, round up */
>         data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length(&delta_next));
>
> -       get_iowait_load(&nr_iowaiters, &cpu_load);
> +       nr_iowaiters = nr_iowait_cpu(dev->cpu);
>         data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);
>
>         /*
> @@ -359,7 +346,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>                  * Use the performance multiplier and the user-configurable
>                  * latency_req to determine the maximum exit latency.
>                  */
> -               interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
> +               interactivity_req = data->predicted_us /
> +                       performance_multiplier(nr_iowaiters);
>                 if (latency_req > interactivity_req)
>                         latency_req = interactivity_req;
>         }
> diff --git a/include/linux/sched/stat.h b/include/linux/sched/stat.h
> index 04f1321..f30954c 100644
> --- a/include/linux/sched/stat.h
> +++ b/include/linux/sched/stat.h
> @@ -20,7 +20,6 @@ extern unsigned long nr_running(void);
>  extern bool single_task_running(void);
>  extern unsigned long nr_iowait(void);
>  extern unsigned long nr_iowait_cpu(int cpu);
> -extern void get_iowait_load(unsigned long *nr_waiters, unsigned long *load);
>
>  static inline int sched_info_on(void)
>  {
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 43efb74..48a786a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2886,13 +2886,6 @@ unsigned long nr_iowait_cpu(int cpu)
>         return atomic_read(&cpu_rq(cpu)->nr_iowait);
>  }
>
> -void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
> -{
> -       struct rq *rq = this_rq();
> -       *nr_waiters = atomic_read(&rq->nr_iowait);
> -       *load = rq->load.weight;
> -}
> -
>  /*
>   * IO-wait accounting, and how its mostly bollocks (on SMP).
>   *
> --
> 2.7.4
>

Re: [PATCH V2 2/2] cpuidle/drivers/menu: Remove get_loadavg in the performance multiplier

[Peter Zijlstra]

On Thu, Oct 04, 2018 at 02:04:03PM +0200, Daniel Lezcano wrote:
> The function get_loadavg() returns almost always zero. To be more
> precise, statistically speaking for a total of 1023379 times passing
> in the function, the load is equal to zero 1020728 times, greater than
> 100, 610 times, the remaining is between 0 and 5.
> 
> In 2011, the get_loadavg() was removed from the Android tree because
> of the above [1]. At this time, the load was:
> 
> unsigned long this_cpu_load(void)
> {
>         struct rq *this = this_rq();
>         return this->cpu_load[0];
> }
> 
> In 2014, the code was changed by commit 372ba8cb46b2 (cpuidle: menu: Lookup CPU
> runqueues less) and the load is:
> 
> void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
> {
>         struct rq *rq = this_rq();
>         *nr_waiters = atomic_read(&rq->nr_iowait);
>         *load = rq->load.weight;
> }
> 
> with the same result.
> 
> Both measurements show using the load in this code path does no matter
> anymore. Removing it.
> 
> [1] https://android.googlesource.com/kernel/common/+/4dedd9f124703207895777ac6e91dacde0f7cc17
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Ramesh Thomas <ramesh.thomas@intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Re: [PATCH V2 1/2] sched: Factor out nr_iowait and nr_iowait_cpu

[Peter Zijlstra]

On Thu, Oct 04, 2018 at 02:04:02PM +0200, Daniel Lezcano wrote:
> The function nr_iowait_cpu() can be used directly by nr_iowait() instead
> of duplicating code.
> 
> Call nr_iowait_cpu() from nr_iowait()
> 
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Re: [PATCH V2 1/2] sched: Factor out nr_iowait and nr_iowait_cpu

[Rafael J. Wysocki]

On Thursday, October 4, 2018 2:04:02 PM CEST Daniel Lezcano wrote:
> The function nr_iowait_cpu() can be used directly by nr_iowait() instead
> of duplicating code.
> 
> Call nr_iowait_cpu() from nr_iowait()
> 
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> ---
>  kernel/sched/core.c | 41 ++++++++++++++++++++---------------------
>  1 file changed, 20 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 625bc98..43efb74 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2875,6 +2875,25 @@ unsigned long long nr_context_switches(void)
>  }
>  
>  /*
> + * Consumers of these two interfaces, like for example the cpufreq menu
> + * governor are using nonsensical data. Boosting frequency for a CPU that has
> + * IO-wait which might not even end up running the task when it does become
> + * runnable.
> + */
> +
> +unsigned long nr_iowait_cpu(int cpu)
> +{
> +	return atomic_read(&cpu_rq(cpu)->nr_iowait);
> +}
> +
> +void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
> +{
> +	struct rq *rq = this_rq();
> +	*nr_waiters = atomic_read(&rq->nr_iowait);
> +	*load = rq->load.weight;
> +}
> +
> +/*
>   * IO-wait accounting, and how its mostly bollocks (on SMP).
>   *
>   * The idea behind IO-wait account is to account the idle time that we could
> @@ -2909,31 +2928,11 @@ unsigned long nr_iowait(void)
>  	unsigned long i, sum = 0;
>  
>  	for_each_possible_cpu(i)
> -		sum += atomic_read(&cpu_rq(i)->nr_iowait);
> +		sum += nr_iowait_cpu(i);
>  
>  	return sum;
>  }
>  
> -/*
> - * Consumers of these two interfaces, like for example the cpufreq menu
> - * governor are using nonsensical data. Boosting frequency for a CPU that has
> - * IO-wait which might not even end up running the task when it does become
> - * runnable.
> - */
> -
> -unsigned long nr_iowait_cpu(int cpu)
> -{
> -	struct rq *this = cpu_rq(cpu);
> -	return atomic_read(&this->nr_iowait);
> -}
> -
> -void get_iowait_load(unsigned long *nr_waiters, unsigned long *load)
> -{
> -	struct rq *rq = this_rq();
> -	*nr_waiters = atomic_read(&rq->nr_iowait);
> -	*load = rq->load.weight;
> -}
> -
>  #ifdef CONFIG_SMP
>  
>  /*
> 

Both [1-2/2] applied with Peter's ACKs, thanks!