Re: [PATCH 5/8] x86/amd: Detect preferred cores in amd_get_boost_ratio_numerator()

[Mario Limonciello <mario.limonciello@amd.com>]

On 8/27/2024 10:43, Gautham R. Shenoy wrote:
> 
> On Mon, Aug 26, 2024 at 04:13:55PM -0500, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> AMD systems that support preferred cores will use "166" as their
>> numerator for max frequency calculations instead of "255".
>>
>> Add a function for detecting preferred cores by looking at the
>> highest perf value on all cores.
>>
>> If preferred cores are enabled return 166 and if disabled the
>> value in the highest perf register. As the function will be called
>> multiple times, cache the values for the boost numerator and if
>> preferred cores will be enabled in global variables.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
> 
> [..snip..]
> 
>>   /**
>>    * amd_get_boost_ratio_numerator: Get the numerator to use for boost ratio calculation
>>    * @cpu: CPU to get numerator for.
>> @@ -162,20 +232,19 @@ EXPORT_SYMBOL_GPL(amd_get_highest_perf);
>>    */
>>   int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator)
>>   {
>> -	struct cpuinfo_x86 *c = &boot_cpu_data;
>> +	bool prefcore;
>> +	int ret;
>>   
>> -	if (c->x86 == 0x17 && ((c->x86_model >= 0x30 && c->x86_model < 0x40) ||
>> -			       (c->x86_model >= 0x70 && c->x86_model < 0x80))) {
>> -		*numerator = 166;
>> -		return 0;
>> -	}
>> +	ret = amd_detect_prefcore(&prefcore);
>> +	if (ret)
>> +		return ret;
>>   
>> -	if (c->x86 == 0x19 && ((c->x86_model >= 0x20 && c->x86_model < 0x30) ||
>> -			       (c->x86_model >= 0x40 && c->x86_model < 0x70))) {
>> -		*numerator = 166;
>> +	/* without preferred cores, return the highest perf register value */
>> +	if (!prefcore) {
>> +		*numerator = boost_numerator;
>>   		return 0;
>>   	}
>> -	*numerator = 255;
>> +	*numerator = CPPC_HIGHEST_PERF_PREFCORE;
> 
> 
> Interesting. So even when the user boots a system that supports
> preferred-cores with "amd_preferred=disable",
> amd_get_boost_ratio_numerator() will return CPPC_HIGHEST_PERF_PREFCORE
> as the call prefcore == true here.
> 
> I suppose that is as intended, since even though the user may not want
> to use the preferred core logic for task-scheduling/load-balancing,
> the numerator for the boost-ratio is purely dependent on the h/w
> capability.
> 
> Is this understanding correct? If so, can this be included as a
> comment in the code ?
> 

Yup, you got it all right.  I'll fold some of this into the function 
comment for v2.

> The rest of the patch looks good to me.
> 
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
> 
> --
> Thanks and Regards
> gautham.
> 
> 
> 
>>   
>>   	return 0;
>>   }
>> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
>> index f470b5700db58..ec32c830abc1d 100644
>> --- a/drivers/cpufreq/amd-pstate.c
>> +++ b/drivers/cpufreq/amd-pstate.c
>> @@ -807,32 +807,18 @@ static DECLARE_WORK(sched_prefcore_work, amd_pstste_sched_prefcore_workfn);
>>   
>>   static void amd_pstate_init_prefcore(struct amd_cpudata *cpudata)
>>   {
>> -	int ret, prio;
>> -	u32 highest_perf;
>> -
>> -	ret = amd_get_highest_perf(cpudata->cpu, &highest_perf);
>> -	if (ret)
>> +	/* user disabled or not detected */
>> +	if (!amd_pstate_prefcore)
>>   		return;
>>   
>>   	cpudata->hw_prefcore = true;
>> -	/* check if CPPC preferred core feature is enabled*/
>> -	if (highest_perf < CPPC_MAX_PERF)
>> -		prio = (int)highest_perf;
>> -	else {
>> -		pr_debug("AMD CPPC preferred core is unsupported!\n");
>> -		cpudata->hw_prefcore = false;
>> -		return;
>> -	}
>> -
>> -	if (!amd_pstate_prefcore)
>> -		return;
>>   
>>   	/*
>>   	 * The priorities can be set regardless of whether or not
>>   	 * sched_set_itmt_support(true) has been called and it is valid to
>>   	 * update them at any time after it has been called.
>>   	 */
>> -	sched_set_itmt_core_prio(prio, cpudata->cpu);
>> +	sched_set_itmt_core_prio((int)READ_ONCE(cpudata->highest_perf), cpudata->cpu);
>>   
>>   	schedule_work(&sched_prefcore_work);
>>   }
>> @@ -998,12 +984,12 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>>   
>>   	cpudata->cpu = policy->cpu;
>>   
>> -	amd_pstate_init_prefcore(cpudata);
>> -
>>   	ret = amd_pstate_init_perf(cpudata);
>>   	if (ret)
>>   		goto free_cpudata1;
>>   
>> +	amd_pstate_init_prefcore(cpudata);
>> +
>>   	ret = amd_pstate_init_freq(cpudata);
>>   	if (ret)
>>   		goto free_cpudata1;
>> @@ -1453,12 +1439,12 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>>   	cpudata->cpu = policy->cpu;
>>   	cpudata->epp_policy = 0;
>>   
>> -	amd_pstate_init_prefcore(cpudata);
>> -
>>   	ret = amd_pstate_init_perf(cpudata);
>>   	if (ret)
>>   		goto free_cpudata1;
>>   
>> +	amd_pstate_init_prefcore(cpudata);
>> +
>>   	ret = amd_pstate_init_freq(cpudata);
>>   	if (ret)
>>   		goto free_cpudata1;
>> @@ -1903,6 +1889,12 @@ static int __init amd_pstate_init(void)
>>   		static_call_update(amd_pstate_update_perf, cppc_update_perf);
>>   	}
>>   
>> +	if (amd_pstate_prefcore) {
>> +		ret = amd_detect_prefcore(&amd_pstate_prefcore);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>>   	/* enable amd pstate feature */
>>   	ret = amd_pstate_enable(true);
>>   	if (ret) {
>> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
>> index 2246ce0630362..1d79320a23490 100644
>> --- a/include/acpi/cppc_acpi.h
>> +++ b/include/acpi/cppc_acpi.h
>> @@ -137,10 +137,12 @@ struct cppc_cpudata {
>>   };
>>   
>>   #ifdef CONFIG_CPU_SUP_AMD
>> +extern int amd_detect_prefcore(bool *detected);
>>   extern int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf);
>>   extern int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator);
>>   #else /* !CONFIG_CPU_SUP_AMD */
>>   static inline int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf) { return -ENODEV; }
>> +static inline int amd_detect_prefcore(bool *detected) { return -ENODEV; }
>>   static inline int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator) { return -ENODEV; }
>>   #endif /* !CONFIG_CPU_SUP_AMD */
>>   
>> -- 
>> 2.43.0
>>