On Fri, Mar 11, 2022 at 9:11 AM z00314508 <[email protected]> wrote:
>
> From: Zucheng Zheng <[email protected]>
>
> On some specific platforms, the cpufreq driver does not define
> cpufreq_driver.get() routine (eg:x86 intel_pstate driver), as a
I guess you mean the cpufreq driver ->get callback.
No, intel_pstate doesn't implement it, because it cannot reliably
return the current CPU frequency.
> result, the cpufreq_get() can't get the correct CPU frequency.
No, it can't, if intel_pstate is the driver, but what's the problem?
This function is only called in one place in the kernel and not on x8
even.
> Modern x86 processors include the hardware needed to accurately
> calculate frequency over an interval -- APERF, MPERF and the TSC.
You can compute the average frequency over an interval, but ->get is
expected to return the actual current frequency at the time call time.
> Here we use arch_freq_get_on_cpu() in preference to any driver
> driver-specific cpufreq_driver.get() routine to get CPU frequency.
>
> Fixes: f8475cef9008 ("x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF")
No kidding.
> Signed-off-by: Zucheng Zheng <[email protected]>
> ---
> drivers/cpufreq/cpufreq.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 80f535cc8a75..d777257b4454 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1806,10 +1806,14 @@ unsigned int cpufreq_get(unsigned int cpu)
> {
> struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> unsigned int ret_freq = 0;
> + unsigned int freq;
>
> if (policy) {
> down_read(&policy->rwsem);
> - if (cpufreq_driver->get)
> + freq = arch_freq_get_on_cpu(policy->cpu);
> + if (freq)
> + ret_freq = freq;
> + else if (cpufreq_driver->get)
Again, what problem exactly does this address?
> ret_freq = __cpufreq_get(policy);
> up_read(&policy->rwsem);
>
> --
On 2022/3/11 23:52, Rafael J. Wysocki wrote:
> On Fri, Mar 11, 2022 at 9:11 AM z00314508 <[email protected]> wrote:
>> From: Zucheng Zheng <[email protected]>
>>
>> On some specific platforms, the cpufreq driver does not define
>> cpufreq_driver.get() routine (eg:x86 intel_pstate driver), as a
> I guess you mean the cpufreq driver ->get callback.
>
> No, intel_pstate doesn't implement it, because it cannot reliably
> return the current CPU frequency.
>
>> result, the cpufreq_get() can't get the correct CPU frequency.
> No, it can't, if intel_pstate is the driver, but what's the problem?
> This function is only called in one place in the kernel and not on x8
> even.
>
>> Modern x86 processors include the hardware needed to accurately
>> calculate frequency over an interval -- APERF, MPERF and the TSC.
> You can compute the average frequency over an interval, but ->get is
> expected to return the actual current frequency at the time call time.
>
>> Here we use arch_freq_get_on_cpu() in preference to any driver
>> driver-specific cpufreq_driver.get() routine to get CPU frequency.
>>
>> Fixes: f8475cef9008 ("x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF")
> No kidding.
>
>> Signed-off-by: Zucheng Zheng <[email protected]>
>> ---
>> drivers/cpufreq/cpufreq.c | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 80f535cc8a75..d777257b4454 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -1806,10 +1806,14 @@ unsigned int cpufreq_get(unsigned int cpu)
>> {
>> struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
>> unsigned int ret_freq = 0;
>> + unsigned int freq;
>>
>> if (policy) {
>> down_read(&policy->rwsem);
>> - if (cpufreq_driver->get)
>> + freq = arch_freq_get_on_cpu(policy->cpu);
>> + if (freq)
>> + ret_freq = freq;
>> + else if (cpufreq_driver->get)
> Again, what problem exactly does this address?
Thank you for review.
In some scenarios, cpufreq driver ->get is not defined,
some driver get the CPU frequency by calling cpufreq_get() will return 0.
The modification to this problem is inspired by the implementation of
the show_scaling_cur_freq().
>
>> ret_freq = __cpufreq_get(policy);
>> up_read(&policy->rwsem);
>>
>> --
> .
>