[RESEND PATCH v2 2/2] arm64/watchdog_hld: Add a cpufreq notifier for update watchdog thresh

[Jie Zhan]

On 19/06/2025 19:48, Yicong Yang wrote:
> From: Yicong Yang <yangyicong at hisilicon.com>
> 
> arm64 depends on the cpufreq driver to gain the maximum cpu frequency
> to convert the watchdog_thresh to perf event period. cpufreq drivers
> like cppc_cpufreq will be initialized lately after the initializing of
> the hard lockup detector so just use a safe cpufreq which will be
> inaccurency. Use a cpufreq notifier to adjust the event's period to
> a more accurate one.
> 
> Signed-off-by: Yicong Yang <yangyicong at hisilicon.com>
> ---
>  arch/arm64/kernel/watchdog_hld.c | 58 ++++++++++++++++++++++++++++++++
>  1 file changed, 58 insertions(+)

In general, this makes the watchdog period closer to the expected.
The actual period might be longer if the cpu maxfreq is lowered down later,
or shorter if boost is turned on later.
LGTM as it's anyhow better than a fixed 5GHz.

Reviewed-by: Jie Zhan <zhanjie9 at hisilicon.com>

> 
> diff --git a/arch/arm64/kernel/watchdog_hld.c b/arch/arm64/kernel/watchdog_hld.c
> index dcd25322127c..e55548cb26df 100644
> --- a/arch/arm64/kernel/watchdog_hld.c
> +++ b/arch/arm64/kernel/watchdog_hld.c
> @@ -34,3 +34,61 @@ bool __init arch_perf_nmi_is_available(void)
>  	 */
>  	return arm_pmu_irq_is_nmi();
>  }
> +
> +static int watchdog_perf_update_period(void *data)
> +{
> +	int cpu = raw_smp_processor_id();
> +	u64 max_cpu_freq, new_period;
> +
> +	max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
> +	if (!max_cpu_freq)
> +		return 0;
> +
> +	new_period = watchdog_thresh * max_cpu_freq;
> +	hardlockup_detector_perf_adjust_period(cpu, new_period);
> +
> +	return 0;
> +}
> +
> +static int watchdog_freq_notifier_callback(struct notifier_block *nb,
> +					   unsigned long val, void *data)
> +{
> +	struct cpufreq_policy *policy = data;
> +	int cpu;
> +
> +	if (val != CPUFREQ_CREATE_POLICY)
> +		return NOTIFY_DONE;
> +
> +	/*
> +	 * Let each online CPU related to the policy update the period by their
> +	 * own. This will serialize with the framework on start/stop the lockup
> +	 * detector (softlockup_{start,stop}_all) and avoid potential race
> +	 * condition. Otherwise we may have below theoretical race condition:
> +	 * (core 0/1 share the same policy)
> +	 * [core 0]                      [core 1]
> +	 *                               hardlockup_detector_event_create()
> +	 *                                 hw_nmi_get_sample_period()
> +	 * (cpufreq registered, notifier callback invoked)
> +	 * watchdog_freq_notifier_callback()
> +	 *   watchdog_perf_update_period()
> +	 *   (since core 1's event's not yet created,
> +	 *    the period is not set)
> +	 *                                 perf_event_create_kernel_counter()
> +	 *                                 (event's period is SAFE_MAX_CPU_FREQ)
> +	 */
> +	for_each_cpu(cpu, policy->cpus)
> +		smp_call_on_cpu(cpu, watchdog_perf_update_period, NULL, false);
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block watchdog_freq_notifier = {
> +	.notifier_call = watchdog_freq_notifier_callback,
> +};
> +
> +static int __init init_watchdog_freq_notifier(void)
> +{
> +	return cpufreq_register_notifier(&watchdog_freq_notifier,
> +					 CPUFREQ_POLICY_NOTIFIER);
> +}
> +core_initcall(init_watchdog_freq_notifier);