linux-kernel - Re: [PATCH v9 1/5] cpufreq: Allow arch_freq_get_on

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Message-ID: <f9606b7c-e20c-43cb-bc03-1deecb0d7539@linux.microsoft.com>
Date: Tue, 21 Jan 2025 16:17:27 +0530
From: Prasanna Kumar T S M <ptsm@...ux.microsoft.com>
To: Beata Michalska <beata.michalska@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
 ionela.voinescu@....com, sudeep.holla@....com, will@...nel.org,
 catalin.marinas@....com, rafael@...nel.org, viresh.kumar@...aro.org
Cc: sumitg@...dia.com, yang@...amperecomputing.com,
 vanshikonda@...amperecomputing.com, lihuisong@...wei.com,
 zhanjie9@...ilicon.com
Subject: Re: [PATCH v9 1/5] cpufreq: Allow arch_freq_get_on_cpu to return an
 error


On 21-01-2025 14:14, Beata Michalska wrote:
> Allow arch_freq_get_on_cpu to return an error for cases when retrieving
> current CPU frequency is not possible, whether that being due to lack of
> required arch support or due to other circumstances when the current
> frequency cannot be determined at given point of time.
>
> Signed-off-by: Beata Michalska <beata.michalska@....com>
> ---
>   arch/x86/kernel/cpu/aperfmperf.c | 2 +-
>   arch/x86/kernel/cpu/proc.c       | 7 +++++--
>   drivers/cpufreq/cpufreq.c        | 8 ++++----
>   include/linux/cpufreq.h          | 2 +-
>   4 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
> index f642de2ebdac..6cf31a1649c4 100644
> --- a/arch/x86/kernel/cpu/aperfmperf.c
> +++ b/arch/x86/kernel/cpu/aperfmperf.c
> @@ -498,7 +498,7 @@ void arch_scale_freq_tick(void)
>    */
>   #define MAX_SAMPLE_AGE	((unsigned long)HZ / 50)
>   
> -unsigned int arch_freq_get_on_cpu(int cpu)
> +int arch_freq_get_on_cpu(int cpu)
>   {
>   	struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
>   	unsigned int seq, freq;
> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index 41ed01f46bd9..d79f5845a463 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>   		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
>   
>   	if (cpu_has(c, X86_FEATURE_TSC)) {
> -		unsigned int freq = arch_freq_get_on_cpu(cpu);
> +		int freq = arch_freq_get_on_cpu(cpu);
>   
> -		seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
> +		if (freq <= 0)
> +			seq_puts(m, "cpu MHz\t\t: Unknown\n");
> +		else
> +			seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
>   	}
>   
>   	/* Cache size */
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 418236fef172..6f45684483c4 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -728,18 +728,18 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
>   show_one(scaling_min_freq, min);
>   show_one(scaling_max_freq, max);
>   
> -__weak unsigned int arch_freq_get_on_cpu(int cpu)
> +__weak int arch_freq_get_on_cpu(int cpu)
>   {
> -	return 0;
> +	return -EOPNOTSUPP;
>   }
>   
>   static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
>   {
>   	ssize_t ret;
> -	unsigned int freq;
> +	int freq;
>   
>   	freq = arch_freq_get_on_cpu(policy->cpu);
> -	if (freq)
> +	if (freq > 0)
>   		ret = sysfs_emit(buf, "%u\n", freq);
>   	else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
>   		ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 7fe0981a7e46..02fd4746231d 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -1184,7 +1184,7 @@ static inline int of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_
>   }
>   #endif
>   
> -extern unsigned int arch_freq_get_on_cpu(int cpu);
> +extern int arch_freq_get_on_cpu(int cpu);
>   
>   #ifndef arch_set_freq_scale
>   static __always_inline

Looks good to me.

Reviewed-by: Prasanna Kumar T S M <ptsm@...ux.microsoft.com>