On 04/10/2018 10:22, Rafael J. Wysocki wrote: > On Thu, Oct 4, 2018 at 9:42 AM 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> >> --- >> 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); > > I wouldn't break this line.
Ok, mind if I break the line in a separate patch before ? (my git pre-commit hook runs checkpatch and it complains and prevent to commit the patch because of the line length (94)). >> 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. >> - */ > > Doesn't the comment still apply to nr_iowait_cpu()? The comment is very confusing. I talks about a cpufreq menu governor and boosting frequency. I don't see this function used in the cpufreq framework but in: kernel/time/tick-sched.c fs/proc/stat.c drivers/cpuidle/governors/menu.c The comment is irrelevant as the remaining function is used for statistics in addition to the perf multiplier. It does exactly what the function name is. >> 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). >> * >> -- -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog