Re: [PATCH 2/2] cpufreq: amd-pstate: Use amd_get_highest_perf() to lookup perf values

Gautham R.Shenoy
2024-06-27T05:13:02Z

Mario Limonciello <mario.limonciello@amd.com> writes:

> To keep consistency with amd-pstate and acpi-cpufreq behavior, use
> amd_get_highest_perf() to find the highest perf value for a given
> platform.
>
> This fixes the exact same problem as commit bf202e654bfa ("cpufreq:
> amd-pstate: fix the highest frequency issue which limits performance")
> from happening on acpi-cpufreq too.
>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> arch/x86/kernel/cpu/amd.c | 16 +++++++++++++++-
> drivers/cpufreq/amd-pstate.c | 21 ++-------------------
> 2 files changed, 17 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 8b730193d79e..e69f640cc248 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -1218,7 +1218,21 @@ u32 amd_get_highest_perf(void)
> }
> }
>

From Patch 1,

+#define CPPC_HIGHEST_PERF_MAX 255
+#define CPPC_HIGHEST_PERF_PERFORMANCE 196
+#define CPPC_HIGHEST_PERF_DEFAULT 166
+

> - return CPPC_HIGHEST_PERF_MAX;
> + /*
> + * 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 (c->x86_model) {
> + case 0x70 ... 0x7f:
> + return CPPC_HIGHEST_PERF_PERFORMANCE;
> + default:
> + return CPPC_HIGHEST_PERF_DEFAULT;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Should this be CPPC_HIGHEST_PERF_MAX ?

Without this patchset, this function returns 255 on Genoa (0x10-0x1f)
and Bergamo (0xa0-0xaf) systems. This patchset changes the return value
to 166.

The acpi-cpufreq driver computes the max frequency based on the
boost-ratio, which is the ratio of the highest_perf (returned by this
function) to the nominal_perf.

So assuming a nominal_freq of 2000Mhz, nominal_perf of 159.

Previously the max_perf = (2000*255/159) ~ 3200Mhz
With this patch max_perf = (2000*166/159) ~ 2100Mhz.

Am I missing something ?

--
Thanks and Regards
gautham.