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. > 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()? > > 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). > * > --