On Thu, Oct 4, 2018 at 2:04 PM Daniel Lezcano <daniel.lezc...@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 <pet...@infradead.org>
> Cc: Todd Kjos <tk...@google.com>
> Cc: Joel Fernandes <joe...@google.com>
> Cc: Colin Cross <ccr...@android.com>
> Cc: Ramesh Thomas <ramesh.tho...@intel.com>
> Cc: Mel Gorman <mgor...@suse.de>
> Signed-off-by: Daniel Lezcano <daniel.lezc...@linaro.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wyso...@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
>
