Re: [PATCH 6/8] cpufreq: amd-pstate: Merge amd_pstate_highest_perf_set() into amd_get_boost_ratio_numerator()

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

Hello Mario,


On Mon, Aug 26, 2024 at 04:13:56PM -0500, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> The special case in amd_pstate_highest_perf_set() is the value used
> for calculating the boost numerator.  Merge this into
> amd_get_boost_ratio_numerator() and then use that to calculate boost
> ratio.
> 
> This allows dropping more special casing of the highest perf value.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>  arch/x86/kernel/acpi/cppc.c  | 16 ++++++++++++
>  drivers/cpufreq/amd-pstate.c | 49 +++++++-----------------------------
>  2 files changed, 25 insertions(+), 40 deletions(-)
> 
> diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
> index 729b35e84f5eb..44b13a4e28740 100644
> --- a/arch/x86/kernel/acpi/cppc.c
> +++ b/arch/x86/kernel/acpi/cppc.c
> @@ -9,6 +9,7 @@
>  #include <asm/processor.h>
>  #include <asm/topology.h>
>  
> +#define CPPC_HIGHEST_PERF_PERFORMANCE	196
>  #define CPPC_HIGHEST_PERF_PREFCORE	166
>  
>  enum amd_pref_core {
> @@ -244,6 +245,21 @@ int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator)
>  		*numerator = boost_numerator;
>  		return 0;
>  	}
> +
> +	/*
> +	 * For AMD CPUs with Family ID 19H and Model ID range 0x70 to 0x7f,
> +	 * the highest performance level is set to 196.
> +	 * https://bugzilla.kernel.org/show_bug.cgi?id=218759
> +	 */
> +	if (cpu_feature_enabled(X86_FEATURE_ZEN4)) {
> +		switch (boot_cpu_data.x86_model) {
> +		case 0x70 ... 0x7f:
> +			*numerator = CPPC_HIGHEST_PERF_PERFORMANCE;
> +			return 0;
> +		default:
> +			break;
> +		}
> +	}
>  	*numerator = CPPC_HIGHEST_PERF_PREFCORE;
>  
>  	return 0;
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index ec32c830abc1d..75568d0f84623 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -52,8 +52,6 @@
>  #define AMD_PSTATE_TRANSITION_LATENCY	20000
>  #define AMD_PSTATE_TRANSITION_DELAY	1000
>  #define AMD_PSTATE_FAST_CPPC_TRANSITION_DELAY 600
> -#define CPPC_HIGHEST_PERF_PERFORMANCE	196
> -#define CPPC_HIGHEST_PERF_DEFAULT	166
>  
>  #define AMD_CPPC_EPP_PERFORMANCE		0x00
>  #define AMD_CPPC_EPP_BALANCE_PERFORMANCE	0x80
> @@ -372,43 +370,17 @@ static inline int amd_pstate_enable(bool enable)
>  	return static_call(amd_pstate_enable)(enable);
>  }
>  
> -static u32 amd_pstate_highest_perf_set(struct amd_cpudata *cpudata)
> -{
> -	struct cpuinfo_x86 *c = &cpu_data(0);
> -
> -	/*
> -	 * For AMD CPUs with Family ID 19H and Model ID range 0x70 to 0x7f,
> -	 * the highest performance level is set to 196.
> -	 * https://bugzilla.kernel.org/show_bug.cgi?id=218759
> -	 */
> -	if (c->x86 == 0x19 && (c->x86_model >= 0x70 && c->x86_model <= 0x7f))
> -		return CPPC_HIGHEST_PERF_PERFORMANCE;
> -
> -	return CPPC_HIGHEST_PERF_DEFAULT;
> -}
> -
>  static int pstate_init_perf(struct amd_cpudata *cpudata)
>  {
>  	u64 cap1;
> -	u32 highest_perf;
>  
>  	int ret = rdmsrl_safe_on_cpu(cpudata->cpu, MSR_AMD_CPPC_CAP1,
>  				     &cap1);
>  	if (ret)
>  		return ret;
>  
> -	/* For platforms that do not support the preferred core feature, the
> -	 * highest_pef may be configured with 166 or 255, to avoid max frequency
> -	 * calculated wrongly. we take the AMD_CPPC_HIGHEST_PERF(cap1) value as
> -	 * the default max perf.
> -	 */
> -	if (cpudata->hw_prefcore)
> -		highest_perf = amd_pstate_highest_perf_set(cpudata);
> -	else
> -		highest_perf = AMD_CPPC_HIGHEST_PERF(cap1);
> -
> -	WRITE_ONCE(cpudata->highest_perf, highest_perf);
> -	WRITE_ONCE(cpudata->max_limit_perf, highest_perf);
> +	WRITE_ONCE(cpudata->highest_perf, AMD_CPPC_HIGHEST_PERF(cap1));
> +	WRITE_ONCE(cpudata->max_limit_perf, AMD_CPPC_HIGHEST_PERF(cap1));


So henceforth, cpudata->highest_perf is expected to cache the value of
CPPC.highest_perf and not the boost_ratio_numerator. There are couple
of user-visible changes due to this.


1.  On platforms where preferred-core is supported, previously the
    sysfs file
    /sys/devices/system/cpu/cpuX/cpufreq/amd_pstate_highest_perf would
    report the boost_ratio_numerator. Henceforth it will report
    CPPC.highest_perf.

    I hope there are no userspace tools that compute the boost_ratio
    using the syfs amd_pstate_highest_perf/amd_pstate_nominal_perf.

2. The amd_pstate_prefcore_ranking and amd_pstate_highest_perf will
   show the same values on all platforms, and henceforth are
   redundant.


Shouldn't this be documented?

The rest of the patch looks good to me.



--
Thanks and Regards
gautham.