Commit a7fe5190 authored by Daniel Lezcano's avatar Daniel Lezcano Committed by Rafael J. Wysocki
Browse files

cpuidle: menu: Remove get_loadavg() from the performance multiplier 

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 372ba8cb (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: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 145d952a

drivers/cpuidle/governors/menu.c

+6 −19
Original line number Diff line number Diff line
@@ -134,11 +134,6 @@ 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;
@@ -172,18 +167,10 @@ 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);
@@ -301,7 +288,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, 
	int idx;

	unsigned int interactivity_req;

	unsigned int predicted_us;

	unsigned long nr_iowaiters, cpu_load;

	unsigned long nr_iowaiters;

	ktime_t delta_next;



	if (data->needs_update) {
@@ -312,7 +299,7 @@ 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);



	if (unlikely(drv->state_count <= 1 || latency_req == 0) ||
@@ -356,7 +343,7 @@ 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 = predicted_us / performance_multiplier(nr_iowaiters, cpu_load);

		interactivity_req = predicted_us / performance_multiplier(nr_iowaiters);

		if (latency_req > interactivity_req)

			latency_req = interactivity_req;

	}

include/linux/sched/stat.h

+0 −1
Original line number Diff line number Diff line
@@ -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)

{

kernel/sched/core.c

+0 −7
Original line number Diff line number Diff line
@@ -2887,13 +2887,6 @@ 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).

 *

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