Re: [PATCH][RFC] sched: cpufreq: Fix long idle judgement logic in load calculation
Hi Viresh, thanks for the comment, On Thu, Jun 07, 2018 at 10:15:43AM +0530, Viresh Kumar wrote: > On 07-06-18, 11:17, Chen Yu wrote: > > diff --git a/drivers/cpufreq/cpufreq_governor.c > > b/drivers/cpufreq/cpufreq_governor.c > > index 871bf9c..9792c80 100644 > > --- a/drivers/cpufreq/cpufreq_governor.c > > +++ b/drivers/cpufreq/cpufreq_governor.c > > @@ -165,7 +165,7 @@ unsigned int dbs_update(struct cpufreq_policy *policy) > > * calls, so the previous load value can be used then. > > */ > > load = j_cdbs->prev_load; > > - } else if (unlikely(time_elapsed > 2 * sampling_rate && > > + } else if (((int)idle_time > 0) && unlikely(idle_time > 2 * > > sampling_rate && > > Yes the figures are insane, but if the idle time is around 36 minutes, the > conversion to int will make a positive value look negative and we will exit > the > conditional block. And if we don't think that we will ever get such insane > idle > times or we don't want to care about them, then what about doing this instead: > > } else if ((unlikely((int)idle_time > 2 * sampling_rate && > > same below. > Yes, this would be more straightforward. Best, Yu > -- > viresh
Re: [PATCH][RFC] sched: cpufreq: Fix long idle judgement logic in load calculation
On 07-06-18, 11:17, Chen Yu wrote: > diff --git a/drivers/cpufreq/cpufreq_governor.c > b/drivers/cpufreq/cpufreq_governor.c > index 871bf9c..9792c80 100644 > --- a/drivers/cpufreq/cpufreq_governor.c > +++ b/drivers/cpufreq/cpufreq_governor.c > @@ -165,7 +165,7 @@ unsigned int dbs_update(struct cpufreq_policy *policy) >* calls, so the previous load value can be used then. >*/ > load = j_cdbs->prev_load; > - } else if (unlikely(time_elapsed > 2 * sampling_rate && > + } else if (((int)idle_time > 0) && unlikely(idle_time > 2 * > sampling_rate && Yes the figures are insane, but if the idle time is around 36 minutes, the conversion to int will make a positive value look negative and we will exit the conditional block. And if we don't think that we will ever get such insane idle times or we don't want to care about them, then what about doing this instead: } else if ((unlikely((int)idle_time > 2 * sampling_rate && same below. -- viresh
[PATCH][RFC] sched: cpufreq: Fix long idle judgement logic in load calculation
According to current code implementation, detecting the long idle period is done by checking if the interval between two adjacent utilization update handers is long enough. Although this mechanism can detect if the idle period is long enough (no utilization hooks invoked during idle period), it might not contain a corner case: if the task has occupied the cpu for too long which causes no context switch during that period, then no utilization handler will be launched until this high prio task is switched out. As a result, the idle_periods field might be calculated incorrectly because it regards the 100% load as 0% and makes the conservative governor who uses this field confusing. Change the judgement to compare the idle_time with sampling_rate directly. Reported-by: Artem S. Tashkinov Cc: Artem S Tashkinov Cc: "Rafael J. Wysocki" Cc: Viresh Kumar Cc: linux...@vger.kernel.org Signed-off-by: Chen Yu --- drivers/cpufreq/cpufreq_governor.c | 12 +--- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index 871bf9c..9792c80 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -165,7 +165,7 @@ unsigned int dbs_update(struct cpufreq_policy *policy) * calls, so the previous load value can be used then. */ load = j_cdbs->prev_load; - } else if (unlikely(time_elapsed > 2 * sampling_rate && + } else if (((int)idle_time > 0) && unlikely(idle_time > 2 * sampling_rate && j_cdbs->prev_load)) { /* * If the CPU had gone completely idle and a task has @@ -185,10 +185,8 @@ unsigned int dbs_update(struct cpufreq_policy *policy) * clear prev_load to guarantee that the load will be * computed again next time. * -* Detecting this situation is easy: the governor's -* utilization update handler would not have run during -* CPU-idle periods. Hence, an unusually large -* 'time_elapsed' (as compared to the sampling rate) +* Detecting this situation is easy: an unusually large +* 'idle_time' (as compared to the sampling rate) * indicates this scenario. */ load = j_cdbs->prev_load; @@ -217,8 +215,8 @@ unsigned int dbs_update(struct cpufreq_policy *policy) j_cdbs->prev_load = load; } - if (time_elapsed > 2 * sampling_rate) { - unsigned int periods = time_elapsed / sampling_rate; + if (((int)idle_time > 0) && (idle_time > 2 * sampling_rate)) { + unsigned int periods = idle_time / sampling_rate; if (periods < idle_periods) idle_periods = periods; -- 2.7.4