| Message ID | 1528420053-22884-1-git-send-email-yu.c.chen@intel.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Delegated to: | Rafael Wysocki |
| Headers | show |
On 08-06-18, 09:07, Chen Yu wrote: > 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 <t.artem@mailcity.com> > Cc: Artem S Tashkinov <t.artem@mailcity.com> > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Cc: linux-pm@vger.kernel.org > Signed-off-by: Chen Yu <yu.c.chen@intel.com> > --- > v2: Per Viresh's suggestion, ignore idle_time longer than 30mins and > simplify the code. > --- > drivers/cpufreq/cpufreq_governor.c | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
On Friday, June 8, 2018 6:04:13 AM CEST Viresh Kumar wrote: > On 08-06-18, 09:07, Chen Yu wrote: > > 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 <t.artem@mailcity.com> > > Cc: Artem S Tashkinov <t.artem@mailcity.com> > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> > > Cc: Viresh Kumar <viresh.kumar@linaro.org> > > Cc: linux-pm@vger.kernel.org > > Signed-off-by: Chen Yu <yu.c.chen@intel.com> > > --- > > v2: Per Viresh's suggestion, ignore idle_time longer than 30mins and > > simplify the code. > > --- > > drivers/cpufreq/cpufreq_governor.c | 12 +++++------- > > 1 file changed, 5 insertions(+), 7 deletions(-) > > Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Patch applied, thanks!
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index 871bf9c..1d50e97 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 (unlikely((int)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 (unlikely((int)idle_time > 2 * sampling_rate)) { + unsigned int periods = idle_time / sampling_rate; if (periods < idle_periods) idle_periods = periods;
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 <t.artem@mailcity.com> Cc: Artem S Tashkinov <t.artem@mailcity.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: linux-pm@vger.kernel.org Signed-off-by: Chen Yu <yu.c.chen@intel.com> --- v2: Per Viresh's suggestion, ignore idle_time longer than 30mins and simplify the code. --- drivers/cpufreq/cpufreq_governor.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)