linux-kernel - Re: [PATCH 2/2] cpufreq: amd-pstate: Use amd_get_highest

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Date: Thu, 27 Jun 2024 00:16:56 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: "Gautham R.Shenoy" <gautham.shenoy@....com>,
 Borislav Petkov <bp@...en8.de>, Perry Yuan <perry.yuan@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
 "H . Peter Anvin" <hpa@...or.com>, Huang Rui <ray.huang@....com>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>,
 Nikolay Borisov <nik.borisov@...e.com>, Peter Zijlstra
 <peterz@...radead.org>,
 "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
 <linux-kernel@...r.kernel.org>,
 "open list:AMD PSTATE DRIVER" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 2/2] cpufreq: amd-pstate: Use amd_get_highest_perf() to
 lookup perf values

On 6/27/2024 00:12, Gautham R.Shenoy wrote:
> Mario Limonciello <mario.limonciello@....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@....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.