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Wysocki" Cc: Russell Haley , "zhenglifeng (A)" , pierre.gondois@arm.com, viresh.kumar@linaro.org, ionela.voinescu@arm.com, corbet@lwn.net, rdunlap@infradead.org, ray.huang@amd.com, gautham.shenoy@amd.com, mario.limonciello@amd.com, perry.yuan@amd.com, zhanjie9@hisilicon.com, linux-pm@vger.kernel.org, linux-acpi@vger.kernel.org, linux-doc@vger.kernel.org, acpica-devel@lists.linux.dev, linux-kernel@vger.kernel.org, linux-tegra@vger.kernel.org, treding@nvidia.com, jonathanh@nvidia.com, vsethi@nvidia.com, ksitaraman@nvidia.com, sanjayc@nvidia.com, nhartman@nvidia.com, bbasu@nvidia.com, sumitg@nvidia.com References: <20260129104817.3752340-1-sumitg@nvidia.com> <20260129104817.3752340-5-sumitg@nvidia.com> <4432fa04-e67c-422a-aae4-2938be431985@huawei.com> <74f3e6cf-7c13-43e6-a8f6-2b46184b8ad6@gmail.com> <944fc140-e5c5-425f-a6ad-883e87eed8a3@nvidia.com> Content-Language: en-US From: Sumit Gupta In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MA5PR01CA0203.INDPRD01.PROD.OUTLOOK.COM (2603:1096:a01:1b0::7) To BN9PR12MB5179.namprd12.prod.outlook.com (2603:10b6:408:11c::18) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN9PR12MB5179:EE_|CY5PR12MB6204:EE_ X-MS-Office365-Filtering-Correlation-Id: 4889bc4a-61e1-4c88-5202-08de6330fecb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024|7053199007; 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Wysocki wrote: > External email: Use caution opening links or attachments > > > On Tue, Feb 3, 2026 at 1:45 PM Rafael J. Wysocki wrote: >> On Tue, Feb 3, 2026 at 10:41 AM Sumit Gupta wrote: >>>>>> Hi Sumit, >>>>>> >>>>>> I am thinking that maybe it is better to call these two sysfs interface >>>>>> 'min_freq' and 'max_freq' as users read and write khz instead of raw >>>>>> value. >>>>> Thanks for the suggestion. >>>>> Kept min_perf/max_perf to match the CPPC register names >>>>> (MIN_PERF/MAX_PERF), making it clear to users familiar with >>>>> CPPC what's being controlled. >>>>> The kHz unit is documented in the ABI. >>>>> >>>>> Thank you, >>>>> Sumit Gupta >>>> On my x86 machine with kernel 6.18.5, the kernel is exposing raw values: >>>> >>>>> grep . /sys/devices/system/cpu/cpu0/acpi_cppc/* >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/feedback_ctrs:ref:342904018856568 >>>> del:437439724183386 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/guaranteed_perf:63 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/highest_perf:88 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/lowest_freq:0 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/lowest_nonlinear_perf:36 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/lowest_perf:1 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/nominal_freq:3900 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/nominal_perf:62 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/reference_perf:62 >>>> /sys/devices/system/cpu/cpu0/acpi_cppc/wraparound_time:18446744073709551615 >>>> >>>> It would be surprising for a nearby sysfs interface with very similar >>>> names to use kHz instead. >>>> >>>> Thanks, >>>> >>>> Russell Haley >>> I can rename to either of the below: >>> - min/max_freq: might be confused with scaling_min/max_freq. >>> - min/max_perf_freq: keeps the CPPC register association clear. >>> >>> Rafael, Any preferences here? >> On x86 the units in CPPC are not kHz and there is no easy reliable way >> to convert them to kHz. >> >> Everything under /sys/devices/system/cpu/cpu0/acpi_cppc/ needs to be >> in CPPC units, not kHz (unless, of course, kHz are CPPC units). In v1 [1], these controls were added under acpi_cppc sysfs. After discussion, they were moved under cpufreq, and [2] was merged first. The decision to use frequency scale instead of raw perf was made for consistency with other cpufreq interfaces as per (v3 [3]). CPPC units in our case are also not in kHz. The kHz conversion uses the existing cppc_perf_to_khz()/cppc_khz_to_perf() helpers which are already used in cppc_cpufreq attributes. So the conversion behavior is consistent with existing cpufreq interfaces. [1] https://lore.kernel.org/lkml/076c199c-a081-4a7f-956c-f395f4d5e156@nvidia.com/ [2] https://lore.kernel.org/all/20250507031941.2812701-1-zhenglifeng1@huawei.com/ [3] https://lore.kernel.org/lkml/80e16de0-63e4-4ead-9577-4ebba9b1a02d@nvidia.com/ > That said, the new attributes will show up elsewhere. > > So why do you need to add these things in the first place? Currently there's no sysfs interface to dynamically control the MIN_PERF/MAX_PERF bounds when using autonomous mode. This helps users tune power and performance at runtime. Thank you, Sumit Gupta