[RESEND PATCH v2 1/2] watchdog/perf: Provide function for adjusting the event period

[Yicong Yang]

On 2025/6/27 23:35, Will Deacon wrote:
> On Thu, Jun 19, 2025 at 07:48:04PM +0800, Yicong Yang wrote:
>> From: Yicong Yang <yangyicong at hisilicon.com>
>>
>> Architecture's using perf events for hard lockup detection needs to
>> convert the watchdog_thresh to the event's period, some architecture
>> for example arm64 perform this conversion using the CPU's maximum
>> frequency which will be acquired by cpufreq. However by the time
>> the lockup detector's initialized the cpufreq driver may not be
>> initialized, thus launch a watchdog with inaccurate period. Provide
>> a function hardlockup_detector_perf_adjust_period() to allowing
>> adjust the event period. Then architecture can update with more
>> accurate period if cpufreq is initialized.
>>
>> Signed-off-by: Yicong Yang <yangyicong at hisilicon.com>
>> ---
>>  include/linux/nmi.h    |  2 ++
>>  kernel/watchdog_perf.c | 23 +++++++++++++++++++++++
>>  2 files changed, 25 insertions(+)
>>
>> diff --git a/include/linux/nmi.h b/include/linux/nmi.h
>> index e78fa535f61d..0a6d8a8d2d5b 100644
>> --- a/include/linux/nmi.h
>> +++ b/include/linux/nmi.h
>> @@ -103,10 +103,12 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs);
>>  extern void hardlockup_detector_perf_stop(void);
>>  extern void hardlockup_detector_perf_restart(void);
>>  extern void hardlockup_config_perf_event(const char *str);
>> +extern void hardlockup_detector_perf_adjust_period(int cpu, u64 period);
>>  #else
>>  static inline void hardlockup_detector_perf_stop(void) { }
>>  static inline void hardlockup_detector_perf_restart(void) { }
>>  static inline void hardlockup_config_perf_event(const char *str) { }
>> +static inline void hardlockup_detector_perf_adjust_period(int cpu, u64 period) { }
>>  #endif
>>  
>>  void watchdog_hardlockup_stop(void);
>> diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c
>> index 75af12ff774e..41c299e63fab 100644
>> --- a/kernel/watchdog_perf.c
>> +++ b/kernel/watchdog_perf.c
>> @@ -186,6 +186,29 @@ void watchdog_hardlockup_disable(unsigned int cpu)
>>  	}
>>  }
>>  
>> +/**
>> + * hardlockup_detector_perf_adjust_period - Adjust the event period due
>> + *                                          to cpu frequency change
>> + * @cpu: The CPU whose event period will be adjusted
>> + * @period: The target period to be set
>> + */
>> +void hardlockup_detector_perf_adjust_period(int cpu, u64 period)
>> +{
>> +	struct perf_event *event = per_cpu(watchdog_ev, cpu);
> 
> Given that this is always called in the context of the current CPU (and
> has to be to avoid the race you describe in the next patch), why not
> drop the 'cpu' argument and use this_cpu_ptr() here instead?
> 

work for me. In v1 this may be called in a remote cpu and I forget to change the
prototype. will drop it, we only have one user to call this on the local cpu.

thanks.