On Thu, 24 Jun 2021 at 12:48, Ionela Voinescu <ionela.voinescu@xxxxxxx> wrote: > > Hi guys, > > On Thursday 24 Jun 2021 at 11:49:53 (+0200), Vincent Guittot wrote: > > On Thu, 24 Jun 2021 at 04:54, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: > > > > > > On 23-06-21, 08:57, Qian Cai wrote: > > > > Viresh, I am afraid I don't feel comfortable yet. I have a few new tests in > > > > development, and will provide an update once ready. > > > > > > Oh sure, np. > > > > > > > Also, I noticed the delivered perf is even smaller than lowest_perf (100). > > > > > > > # cat /sys/devices/system/cpu/cpu8/acpi_cppc/feedback_ctrs > > > > ref:103377547901 del:54540736873 > > > > # cat /sys/devices/system/cpu/cpu8/acpi_cppc/feedback_ctrs > > > > ref:103379170101 del:54541599117 > > > > > > > > 100 * (54541599117 - 54540736873) / (103379170101 - 103377547901) = 53 > > > > I'm not sure that I understand your point. The formula above says that > > cpu8 run @ 53% of nominal performance > > > > I think this is based on a previous example Qian had where: > > /sys/devices/system/cpu/cpu0/acpi_cppc/highest_perf > 300 > /sys/devices/system/cpu/cpu0/acpi_cppc/lowest_freq > 1000 > /sys/devices/system/cpu/cpu0/acpi_cppc/lowest_perf > 100 > /sys/devices/system/cpu/cpu0/acpi_cppc/reference_perf > 100 > > ..so the 100 is not from obtaining percentage, is the reference > performance. > > The logic of the formula is to obtain the delivered performance when > knowing the number of ticks for each counter, so: > > So if one gets (103379170101 - 103377547901) ticks for the counter at > running at 1GHz(perf 100), what is the frequency of the core, if its > counter ticked (54541599117 - 54540736873) times in the same interval > of time? > > The answer is 530MHz(perf 53), which is lower than the lowest frequency > at 1GHz(perf 100). But the nominal_perf is 280 and not 100 if i'm not wrong so the perf value is 148 > lowest_perf in this case > > > > > > > > > > My understanding is that the delivered perf should fail into the range between > > > > lowest_perf and highest_perf. Is that assumption correct? This happens on > > > > 5.4-based kernel, so I am in process running your series on that system to see > > > > if there is any differences. In any case, if it is a bug it is pre-existing, > > > > but I'd like to understand a bit better in that front first. > > > > > > Vincent: > > > > > > Can that happen because of CPU idle ? > > > > > Not if the counters are implemented properly. The kernel considers that > both reference and delivered performance counters should stop or reset > during idle. The kernel would not account for idle itself. > > If the reference performance counter does not stop during idle, while > the core performance counter (delivered) does stop, the behavior above > should be seen very often. > > Qian, do you see these small delivered performance values often or > seldom? > > Thanks, > Ionela. > > > > -- > > > viresh
