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

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Message-ID: <f605de1c-fa8b-c178-46f2-f27b304e6e66@huawei.com>
Date:   Thu, 26 Oct 2023 11:21:34 +0800
From:   Zeng Heng <zengheng4@...wei.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     <broonie@...nel.org>, <joey.gouly@....com>, <will@...nel.org>,
        <amit.kachhap@....com>, <rafael@...nel.org>,
        <catalin.marinas@....com>, <james.morse@....com>, <maz@...nel.org>,
        <viresh.kumar@...aro.org>, <sumitg@...dia.com>,
        <yang@...amperecomputing.com>, <linux-kernel@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <wangxiongfeng2@...wei.com>, <xiexiuqi@...wei.com>,
        Ionela Voinescu <ionela.voinescu@....com>
Subject: Re: [PATCH 2/3] cpufreq: CPPC: Keep the target core awake when
 reading its cpufreq rate


在 2023/10/25 18:54, Mark Rutland 写道:
> [adding Ionela]
>
> 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.
> IIUC there's a pretty deliberate split with all the actual reading of the AMU
> living in arch/arm64/kernel/topolgy.c, and the driver code being (relatively)
> generic.
>
> We already have code in arch/arm64/kernel/topolgy.c to read counters on a
> specific CPU; why can't e reuse that (and avoid exporting cpu_has_amu_feat())?
>
> Mark.

In this scenario, both topology.c and cppc_acpi.c do not provide an API 
to keep the AMU online

during the whole sampling period. Just using cpc_read_ffh at the start 
and end of the sampling

period is not enough.

However, I can propose cpc_ffh_supported() function to replace the 
cpu_has_amu_feat() as v2

if you think this patch set is still valuable.


Thanks,

Zeng Heng

>> Reported-by: Sumit Gupta <sumitg@...dia.com>
>> Link: https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/
>> Signed-off-by: Zeng Heng <zengheng4@...wei.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
>> @@ -90,6 +90,12 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
>>   				 struct cppc_perf_fb_ctrs *fb_ctrs_t0,
>>   				 struct cppc_perf_fb_ctrs *fb_ctrs_t1);
>>   
>> +struct fb_ctr_pair {
>> +	u32 cpu;
>> +	struct cppc_perf_fb_ctrs fb_ctrs_t0;
>> +	struct cppc_perf_fb_ctrs fb_ctrs_t1;
>> +};
>> +
>>   /**
>>    * cppc_scale_freq_workfn - CPPC arch_freq_scale updater for frequency invariance
>>    * @work: The work item.
>> @@ -840,9 +846,24 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
>>   	return (reference_perf * delta_delivered) / delta_reference;
>>   }
>>   
>> +static int cppc_get_perf_ctrs_pair(void *val)
>> +{
>> +	struct fb_ctr_pair *fb_ctrs = val;
>> +	int cpu = fb_ctrs->cpu;
>> +	int ret;
>> +
>> +	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t0);
>> +	if (ret)
>> +		return ret;
>> +
>> +	udelay(2); /* 2usec delay between sampling */
>> +
>> +	return cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t1);
>> +}
>> +
>>   static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>   {
>> -	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
>> +	struct fb_ctr_pair fb_ctrs = { .cpu = cpu, };
>>   	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
>>   	struct cppc_cpudata *cpu_data = policy->driver_data;
>>   	u64 delivered_perf;
>> @@ -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))
>> +		ret = smp_call_on_cpu(cpu, cppc_get_perf_ctrs_pair,
>> +				      &fb_ctrs, false);
>> +	else
>> +		ret = cppc_get_perf_ctrs_pair(&fb_ctrs);
>>   
>> -	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
>>   	if (ret)
>>   		return 0;
>>   
>> -	delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
>> -					       &fb_ctrs_t1);
>> +	delivered_perf = cppc_perf_from_fbctrs(cpu_data,
>> +					      &fb_ctrs.fb_ctrs_t0,
>> +					      &fb_ctrs.fb_ctrs_t1);
>>   
>>   	return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
>>   }
>> -- 
>> 2.25.1
>>