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Date: Thu, 4 Oct 2018 09:42:07 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: rafael@...nel.org
Cc: rjw@...ysocki.net, linux-pm@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Todd Kjos <tkjos@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
Colin Cross <ccross@...roid.com>,
Ramesh Thomas <ramesh.thomas@...el.com>,
Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Alex Shi <alex.shi@...aro.org>,
Philippe Ombredanne <pombredanne@...b.com>,
Thomas Gleixner <tglx@...utronix.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kate Stewart <kstewart@...uxfoundation.org>,
linux-kernel@...r.kernel.org (open list)
Subject: [PATCH 2/2] cpuidle/drivers/menu: Remove get_loadavg in 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 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@...radead.org>
Cc: Todd Kjos <tkjos@...gle.com>
Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Colin Cross <ccross@...roid.com>
Cc: Ramesh Thomas <ramesh.thomas@...el.com>
Cc: Mel Gorman <mgorman@...e.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
---
drivers/cpuidle/governors/menu.c | 26 +++++++-------------------
include/linux/sched/stat.h | 1 -
kernel/sched/core.c | 13 -------------
3 files changed, 7 insertions(+), 33 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 b88a145..5605f03 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2873,25 +2873,12 @@ unsigned long long nr_context_switches(void)
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)
{
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
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