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

Message ID 1538654644-32705-1-git-send-email-daniel.lezcano@linaro.org
State New
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  • [V2,1/2] sched: Factor out nr_iowait and nr_iowait_cpu
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Commit Message

Daniel Lezcano Oct. 4, 2018, 12:04 p.m.
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(-)

-- 
2.7.4

Comments

Mel Gorman Oct. 4, 2018, 12:28 p.m. | #1
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
Rafael J. Wysocki Oct. 4, 2018, 3:23 p.m. | #2
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

>
Peter Zijlstra Oct. 12, 2018, 8:28 a.m. | #3
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>
Peter Zijlstra Oct. 12, 2018, 8:28 a.m. | #4
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>
Rafael J. Wysocki Oct. 26, 2018, 9:22 a.m. | #5
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!

Patch

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
 
 /*