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

Gautham R. Shenoy
2024-08-27T16:53:03Z

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.