On 06/21/2017 11:47 AM, Liang, Kan wrote:
>
>
>> On Wed, 21 Jun 2017, kan.liang@xxxxxxxxx wrote:
>>>
>>> #ifdef CONFIG_HARDLOCKUP_DETECTOR
>>> +/*
>>> + * The NMI watchdog relies on PERF_COUNT_HW_CPU_CYCLES event,
>> which
>>> + * can tick faster than the measured CPU Frequency due to Turbo mode.
>>> + * That can lead to spurious timeouts.
>>> + * To workaround the issue, extending the period by 3 times.
>>> + */
>>> u64 hw_nmi_get_sample_period(int watchdog_thresh) {
>>> - return (u64)(cpu_khz) * 1000 * watchdog_thresh;
>>> + return (u64)(cpu_khz) * 1000 * watchdog_thresh * 3;
>>
>> The maximum turbo frequency of any given machine can be retrieved.
>
> The maximum turbo frequency is determined by the model of processor.
> I'm not sure if there is a generic way to get the maximum turbo frequency.
> Is there?
>
cpufreq_quick_get_max()
but iff cpufreq subsystem is initialized. O/w 0 is returned for the freq.
Quick test shows the correct turbo max of 3700000 on my 2000000 (2.00GHz)
system.
P.
> Thanks,
> Kan
>
>>
>> So why don't you simply take that ratio into account and apply it for the
>> machines which have those insane turbo loaders? That's not a huge effort,
>> can be easily backported and does not inflict this unconditially.
>>
>> So what you want is:
>>
>> return get_max_turbo_khz() * 1000 * watchdog_thresh;
>>
>> Where get_max_turbo_khz() by default returns cpu_khz for non turbo
>> motors.
>>
>> And instead of silently doing this it should emit a info into dmesg:
>>
>> u64 period, max_khz = get_max_turbo_khz();
>> static int once;
>>
>> period = max_khz * 1000 * watchdog_thresh;
>>
>> if (max_khz != cpu_khz && !once) {
>> unsigned int msec = period / cpu_khz;
>>
>> once = 1;
>> pr_info("Adjusted watchdog threshold to %u.%04u sec\n",
>> msec / 1000, msec % 1000);
>> }
>>
>> return period;
>>
>> Hmm?
>>
>> Thanks,
>>
>> tglx
>