[PATCH 2/3] cpufreq: CPPC: Keep the target core awake when reading its cpufreq rate

[Zeng Heng]

在 2023/10/25 19:13, Sudeep Holla 写道:
> On Wed, Oct 25, 2023 at 05:38:46PM +0800, Zeng Heng wrote:
>> As ARM AMU's document says, all counters are subject to any changes
>> in clock frequency, including clock stopping caused by the WFI and WFE
>> instructions.
>>
>> Therefore, using smp_call_on_cpu() to trigger target CPU to
>> read self's AMU counters, which ensures the counters are working
>> properly while cstate feature is enabled.
>>
>> Reported-by: Sumit Gupta <sumitg at nvidia.com>
>> Link: https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/
>> Signed-off-by: Zeng Heng <zengheng4 at huawei.com>
>> ---
>>   drivers/cpufreq/cppc_cpufreq.c | 39 ++++++++++++++++++++++++++--------
>>   1 file changed, 30 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>> index fe08ca419b3d..321a9dc9484d 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
> [...]
>
>> @@ -850,18 +871,18 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>   
>>   	cpufreq_cpu_put(policy);
>>   
>> -	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
>> -	if (ret)
>> -		return 0;
>> -
>> -	udelay(2); /* 2usec delay between sampling */
>> +	if (cpu_has_amu_feat(cpu))
> Have you compiled this on x86 ? Even if you have somehow managed to,
> this is not the right place to check the presence of AMU feature on
> the CPU.
> If AMU registers are used in CPPC, they must be using FFH GAS, in which
> case the interpretation of FFH is architecture dependent code.


According to drivers/cpufreq/Makefile, cppc_cpufreq.c is only compiled with

ARM architecture.

But here, I would change cpu_has_amu_feat() with cpc_ffh_supported(), which

belongs to FFH APIs.

Thanks for the suggestion.


Thanks again,

Zeng Heng



> --
> Regards,
> Sudeep
>