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

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Message-ID: <87msn7ezoz.fsf@BLR-5CG11610CF.amd.com>
Date: Thu, 27 Jun 2024 10:42:44 +0530
From: Gautham R.Shenoy <gautham.shenoy@....com>
To: Mario Limonciello <mario.limonciello@....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>, Mario Limonciello <mario.limonciello@....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

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 ?


--
Thanks and Regards
gautham.