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

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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 372ba8cb46 (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] 4dedd9f124

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Daniel Lezcano 2018-10-04 14:04:03 +02:00 committed by Rafael J. Wysocki
parent 145d952a29
commit a7fe5190c0
3 changed files with 6 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
drivers/cpuidle/governors/menu.c
View File

@ -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;
}

1
include/linux/sched/stat.h
View File

@ -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)
{

7
kernel/sched/core.c
View File

@ -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).
*