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From: "Fontenot, Nathan" <Nathan.Fontenot@amd.com>
To: Huang Rui <ray.huang@amd.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Borislav Petkov <bp@suse.de>, Ingo Molnar <mingo@kernel.org>,
	linux-pm@vger.kernel.org
Cc: Deepak Sharma <deepak.sharma@amd.com>,
	Alex Deucher <alexander.deucher@amd.com>,
	Mario Limonciello <mario.limonciello@amd.com>,
	Jinzhou Su <Jinzhou.Su@amd.com>,
	Xiaojian Du <Xiaojian.Du@amd.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH 04/19] cpufreq: amd: introduce a new amd pstate driver to support future processors
Date: Thu, 9 Sep 2021 14:31:26 -0500	[thread overview]
Message-ID: <c9601b78-10ce-e4c1-6056-3d1922c0ed41@amd.com> (raw)
In-Reply-To: <20210908150001.3702552-5-ray.huang@amd.com>


On 9/8/2021 9:59 AM, Huang Rui wrote:
> amd-pstate is the AMD CPU performance scaling driver that introduces a
> new CPU frequency control mechanism on AMD Zen based CPU series in Linux
> kernel. The new mechanism is based on Collaborative processor
> performance control (CPPC) which is finer grain frequency management
> than legacy ACPI hardware P-States. Current AMD CPU platforms are using
> the ACPI P-states driver to manage CPU frequency and clocks with
> switching only in 3 P-states. AMD P-States is to replace the ACPI
> P-states controls, allows a flexible, low-latency interface for the
> Linux kernel to directly communicate the performance hints to hardware.
>

This patch seems like it is just enabling CPPC on AMD and not a new mechanism
based on CPPC. Can you clarify?

Also, if this is just enabling CPPC, shouldn't the driver be named something
like amd_cppc and not amd_pstate? This isn't using P-states.
 
> "amd-pstate" leverages the Linux kernel governors such as *schedutil*,
> *ondemand*, etc. to manage the performance hints which are provided by CPPC
> hardware functionality. The first version for amd-pstate is to support one
> of the Zen3 processors, and we will support more in future after we verify
> the hardware and SBIOS functionalities.
> 
> There are two types of hardware implementations for amd-pstate: one is full
> MSR support and another is shared memory support. It can use
> X86_FEATURE_AMD_CPPC_EXT feature flag to distinguish the different types.
>

Looking at the drivers/acpi code for CPPC I don't think this distinction
between MSRs and shared memory requires a feature flag. Shouldn't this be
handled properly in cpc_read|write if the ACPI tables are set up correctly?
Please correct me if I'm wrong.

This would also remove the need for the additional indirection pointed
out by Peter.

Could you also provide an explanation as to why a new CPPC driver is need
instead of updating the existing cppc_cpufreq driver.

-Nathan

  parent reply	other threads:[~2021-09-09 19:31 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08 14:59 [PATCH 00/19] cpufreq: introduce a new AMD CPU frequency control mechanism Huang Rui
2021-09-08 14:59 ` [PATCH 01/19] x86/cpufreatures: add AMD CPPC extension feature flag Huang Rui
2021-09-08 20:00   ` Shuah Khan
2021-09-09  9:45     ` Huang Rui
2021-09-09 17:58   ` Borislav Petkov
2021-09-13  9:48     ` Huang Rui
2021-09-13 13:04       ` Borislav Petkov
2021-09-16  9:30         ` Huang Rui
2021-09-08 14:59 ` [PATCH 02/19] x86/msr: add AMD CPPC MSR definitions Huang Rui
2021-09-08 14:59 ` [PATCH 03/19] ACPI: CPPC: add cppc enable register function Huang Rui
2021-09-08 19:14   ` Fontenot, Nathan
2021-09-09  9:50     ` Huang Rui
2021-09-09  0:21   ` Shuah Khan
2021-09-09  9:58     ` Huang Rui
2021-09-08 14:59 ` [PATCH 04/19] cpufreq: amd: introduce a new amd pstate driver to support future processors Huang Rui
2021-09-09 15:01   ` Peter Zijlstra
2021-09-13  8:11     ` Huang Rui
2021-09-13  8:56       ` Peter Zijlstra
2021-09-13 10:54         ` Huang Rui
2021-09-13 11:56           ` Peter Zijlstra
2021-09-16 10:09             ` Huang Rui
2021-09-16 11:19               ` Rafael J. Wysocki
2021-09-17  3:41                 ` Huang Rui
2021-09-09 15:03   ` Peter Zijlstra
2021-09-13 11:55     ` Huang Rui
2021-09-09 19:31   ` Fontenot, Nathan [this message]
2021-09-13 11:18     ` Huang Rui
2021-09-08 14:59 ` [PATCH 05/19] cpufreq: amd: add fast switch function for amd-pstate module Huang Rui
2021-09-08 14:59 ` [PATCH 06/19] cpufreq: amd: add acpi cppc function as the backend for legacy processors Huang Rui
2021-09-08 14:59 ` [PATCH 07/19] cpufreq: amd: add trace for amd-pstate module Huang Rui
2021-09-08 14:59 ` [PATCH 08/19] cpufreq: amd: add boost mode support for amd-pstate Huang Rui
2021-09-08 18:24   ` Fontenot, Nathan
2021-09-09 10:12     ` Huang Rui
2021-09-08 14:59 ` [PATCH 09/19] cpufreq: amd: add amd-pstate checking support check attribute Huang Rui
2021-09-08 14:59 ` [PATCH 10/19] cpufreq: amd: add amd-pstate frequencies attributes Huang Rui
2021-09-08 18:13   ` Fontenot, Nathan
2021-09-08 14:59 ` [PATCH 11/19] cpufreq: amd: add amd-pstate performance attributes Huang Rui
2021-09-08 18:20   ` Fontenot, Nathan
2021-09-08 14:59 ` [PATCH 12/19] cpupower: add AMD P-state capability flag Huang Rui
2021-09-08 14:59 ` [PATCH 13/19] cpupower: add the function to check amd-pstate enabled Huang Rui
2021-09-09 22:16   ` Shuah Khan
2021-09-13 11:29     ` Huang Rui
2021-09-08 14:59 ` [PATCH 14/19] cpupower: initial AMD P-state capability Huang Rui
2021-09-09 22:16   ` Shuah Khan
2021-09-13 12:58     ` Huang Rui
2021-09-08 14:59 ` [PATCH 15/19] cpupower: add amd-pstate sysfs entries into libcpufreq Huang Rui
2021-09-09 22:26   ` Shuah Khan
2021-09-16  8:47     ` Huang Rui
2021-09-08 14:59 ` [PATCH 16/19] cpupower: enable boost state support for amd-pstate module Huang Rui
2021-09-08 17:32   ` Fontenot, Nathan
2021-09-09  9:59     ` Huang Rui
2021-09-09 22:42   ` Shuah Khan
2021-09-16  9:27     ` Huang Rui
2021-09-08 14:59 ` [PATCH 17/19] cpupower: add amd-pstate get data function to query the info Huang Rui
2021-09-09 22:45   ` Shuah Khan
2021-09-08 15:00 ` [PATCH 18/19] cpupower: print amd-pstate information on cpupower Huang Rui
2021-09-09 22:46   ` Shuah Khan
2021-09-16  9:29     ` Huang Rui
2021-09-08 15:00 ` [PATCH 19/19] Documentation: amd-pstate: add amd-pstate driver introduction Huang Rui

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