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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, 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> <211d9dfa-26e6-4fc3-b70b-f5fbca49e5fd@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: MA5P287CA0037.INDP287.PROD.OUTLOOK.COM (2603:1096:a01:175::17) To BN9PR12MB5179.namprd12.prod.outlook.com (2603:10b6:408:11c::18) Precedence: bulk X-Mailing-List: linux-tegra@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN9PR12MB5179:EE_|MN2PR12MB4239:EE_ X-MS-Office365-Filtering-Correlation-Id: 9db859f6-a175-419b-8718-08de63d2f4fb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024|18082099003; 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Wysocki wrote: >> On Tue, Feb 3, 2026 at 3:32 PM Sumit Gupta wrote: >>> >>> >>> On 03/02/26 18:24, Rafael J. 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. >> >> So what about scaling_min_freq and scaling_max_freq? >> >> intel_pstate uses them for an analogous purpose. > > FWIW same thing for amd_pstate. > intel_pstate and amd_pstate seem to use setpolicy() to update scaling_min/max_freq and program MIN_PERF/MAX_PERF. However, as discussed in v5 [1], cppc_cpufreq cannot switch to a setpolicy based approach because: - We need per-CPU control of auto_sel: With setpolicy, we can't   dynamically disable auto_sel for individual CPUs and return to the   target() (no target hook available).   intel_pstate and amd_pstate seem to set HW autonomous mode for   all CPUs, not per-CPU. - We need to retain the target() callback - the CPPC spec allows   desired_perf to be used even when autonomous selection is enabled. [1] https://lore.kernel.org/lkml/66f58f43-631b-40a0-8d42-4e90cd24b757@arm.com/ Thank You, Sumit Gupta