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

Mario Limonciello
2024-06-27T05:17:02Z

On 6/27/2024 00:12, Gautham R.Shenoy wrote:
> 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 ?

Yeah; this is exactly what I'm worried about.

How does Bergamo handle amd-pstate? It should probably explode there too.