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Shenoy" , Perry Yuan Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "open list:CPU FREQUENCY SCALING FRAMEWORK" , Mario Limonciello References: <20250217220707.1468365-1-superm1@kernel.org> <20250217220707.1468365-5-superm1@kernel.org> <9db9da8f-859d-4e23-94ca-e14905c8c6c7@kernel.org> Content-Language: en-US From: Dhananjay Ugwekar In-Reply-To: <9db9da8f-859d-4e23-94ca-e14905c8c6c7@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SG2PR02CA0130.apcprd02.prod.outlook.com (2603:1096:4:188::8) To LV8PR12MB9207.namprd12.prod.outlook.com (2603:10b6:408:187::15) 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: LV8PR12MB9207:EE_|PH8PR12MB7326:EE_ X-MS-Office365-Filtering-Correlation-Id: 32a12695-7448-4457-6eef-08dd5554e73d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; 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Shenoy >>> Signed-off-by: Mario Limonciello >>> --- >>> v3: >>>   * Pick up tag >>> v2: >>>   * cache perf variable in unit tests >>>   * Drop unnecessary check from amd_pstate_update_min_max_limit() >>>   * Consistency with READ_ONCE() >>>   * Drop unneeded policy checks >>>   * add kdoc >>> --- >>>   drivers/cpufreq/amd-pstate-ut.c |  18 +-- >>>   drivers/cpufreq/amd-pstate.c    | 195 ++++++++++++++++++-------------- >>>   drivers/cpufreq/amd-pstate.h    |  49 +++++--- >>>   3 files changed, 151 insertions(+), 111 deletions(-) >>> [Snip] >>> + *          calculated wrongly. we take the fixed value as the highest_perf. >>> + * @nominal_perf: the maximum sustained performance level of the processor, >>> + *          assuming ideal operating conditions >>> + * @lowest_nonlinear_perf: the lowest performance level at which nonlinear power >>> + *               savings are achieved >>> + * @lowest_perf: the absolute lowest performance level of the processor >>> + * @min_limit_perf: Cached value of the performance corresponding to policy->min >>> + * @max_limit_perf: Cached value of the performance corresponding to policy->max >>> + */ >>> +union perf_cached { >>> +    struct { >>> +        u8    highest_perf; >>> +        u8    nominal_perf; >>> +        u8    lowest_nonlinear_perf; >>> +        u8    lowest_perf; >>> +        u8    min_limit_perf; >>> +        u8    max_limit_perf; >> >> Just a thought, how about adding the "u8 desired_perf" (last requested) and "u8 prefcore_ranking" >> in this. We can pursue it as a separate patch if you want. >> >> I think there is value in adding desired_perf atleast, so that when we are caching the >> min, max limits in the perf_cached variable, desired perf level is also atomically >> updated into the shared cpudata structure. > > Can you see if there is any performance advantage to caching these? > If there is, can you please do a follow up to my v5 series? There might not be a performance advantage, but I thought it will tie up the entire perf updation (min, max, des) into one atomic write to perf_cached. But the min, max and des_perf updation is divided into different functions currently. So it may not work as I'm imagining. > > It's going to mean another write in amd_pstate_update() potentially. Yea, right, I'll investigate and see if it is worth doing. > >> >> Thanks, >> Dhananjay