2016-05-04 19:41 GMT+08:00 Rafael J. Wysocki <[email protected]>: > On Wed, May 4, 2016 at 2:53 AM, Wanpeng Li <[email protected]> wrote: >> 2016-05-03 21:33 GMT+08:00 Rafael J. Wysocki <[email protected]>: >>> On Tue, May 3, 2016 at 11:25 AM, Wanpeng Li <[email protected]> wrote: >>>> 2016-05-03 17:19 GMT+08:00 Wanpeng Li <[email protected]>: >>>>> 2016-05-03 16:32 GMT+08:00 Peter Zijlstra <[email protected]>: >>>>>> On Tue, May 03, 2016 at 09:10:51AM +0800, kernel test robot wrote: > > [cut] > >>>>> ----snip---- >>>>> >>>>> diff --git a/drivers/cpufreq/intel_pstate.c >>>>> b/drivers/cpufreq/intel_pstate.c >>>>> index 8b5a415..57b3843 100644 >>>>> --- a/drivers/cpufreq/intel_pstate.c >>>>> +++ b/drivers/cpufreq/intel_pstate.c >>>>> @@ -1241,6 +1241,7 @@ static int intel_pstate_init_cpu(unsigned int >>>>> cpunum) >>>>> intel_pstate_get_cpu_pstates(cpu); >>>>> >>>>> intel_pstate_busy_pid_reset(cpu); >>>>> + intel_pstate_sample(cpu); >>>> >>>> intel_pstate_sample(cpu, 0); >>>> >>>>> >>>>> cpu->update_util.func = intel_pstate_update_util; >>> >>> That would avoid the divide by 0, but the value returned by >>> intel_pstate_get() would still be bogus. >> >> If your bogus means that some data is stale and could you explain more? > > get_avg_frequency() expects sample.aperf to be a delta between two > different values of the APERF register obtained at two different > instants of time, and analogously for sample.mperf, because that's > when the formula used by it is guaranteed to be valid. This means > that it generally is not sufficient to read those registers just once > to get a meaningful result, they need to be read at least twice for > that (with some time between the reads to let the counters grow > sufficiently). > > With your modification sample.aperf and sample.mperf would simply > contain the values of APERF and MPERF, respectively, at the the > intel_pstate_sample(cpu, 0) invocation time, so using them in the > computation would not be guaranteed to lead to a meaningful result.
I see, thanks Rafael. Regards, Wanpeng Li
