From 800bf05db86a2e29b56e4c3b2644e62ffa00d059 Mon Sep 17 00:00:00 2001 From: Daniel Lezcano Date: Thu, 4 Oct 2018 14:04:03 +0200 Subject: [PATCH 1468/2944] cpuidle: menu: Remove get_loadavg() from the performance multiplier to #28739709 commit a7fe5190c03f8137ef08db84a58dd4daf2c4785d upstream 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 Signed-off-by: Daniel Lezcano Acked-by: Mel Gorman Acked-by: Peter Zijlstra (Intel) Signed-off-by: Rafael J. Wysocki Signed-off-by: Yihao Wu Reviewed-by: Shanpei Chen --- drivers/cpuidle/governors/menu.c | 26 ++++++++------------------ include/linux/sched/stat.h | 1 - kernel/sched/core.c | 7 ------- 3 files changed, 8 insertions(+), 26 deletions(-) diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index add0ac3..744241a 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -130,10 +130,8 @@ struct menu_device { int interval_ptr; }; -static inline int get_loadavg(unsigned long load) -{ - return LOAD_INT(load) * 10 + LOAD_FRAC(load) / 10; -} +#define LOAD_INT(x) ((x) >> FSHIFT) +#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100) static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters) { @@ -168,18 +166,10 @@ 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); @@ -285,7 +275,7 @@ 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) { @@ -302,7 +292,7 @@ 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); /* @@ -354,7 +344,7 @@ 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 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 db28707..cbdf0ee 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(&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 /* -- 1.8.3.1