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

["Gautham R. Shenoy" <gautham.shenoy@amd.com>]

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 ?

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
>