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Peter Anvin" , "Rafael J . Wysocki" , "Gautham R . Shenoy" , Perry Yuan , Brijesh Singh , Li RongQing , "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "open list:ACPI" , "open list:AMD PSTATE DRIVER" , Pawan Gupta References: <20241130140703.557-1-mario.limonciello@amd.com> <20241130140703.557-10-mario.limonciello@amd.com> <20241202155951.GH35539@noisy.programming.kicks-ass.net> Content-Language: en-US From: Mario Limonciello In-Reply-To: <20241202155951.GH35539@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SA9PR13CA0027.namprd13.prod.outlook.com (2603:10b6:806:21::32) To MN0PR12MB6101.namprd12.prod.outlook.com (2603:10b6:208:3cb::10) 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: MN0PR12MB6101:EE_|SN7PR12MB7854:EE_ X-MS-Office365-Filtering-Correlation-Id: a0fcf04c-755a-48fc-60ac-08dd13e55c8e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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Specifically, when a task >> is switched in, the class ID was read and reset the hardware workload >> classification history of CPU firmware and then it start to trigger >> workload classification for the next running thread. >> >> Signed-off-by: Perry Yuan >> Co-developed-by: Mario Limonciello >> Signed-off-by: Mario Limonciello >> --- > >> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c >> index 226472332a70d..371e0e8f987fa 100644 >> --- a/arch/x86/kernel/process_64.c >> +++ b/arch/x86/kernel/process_64.c >> @@ -709,6 +709,10 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) >> /* Load the Intel cache allocation PQR MSR. */ >> resctrl_sched_in(next_p); >> >> + /* Reset hw history on AMD CPUs */ >> + if (cpu_feature_enabled(X86_FEATURE_AMD_WORKLOAD_CLASS)) >> + wrmsrl(AMD_WORKLOAD_HRST, 0x1); >> + >> return prev_p; >> } > > BTW, how many cycles for this WRMSR ? When I measured it the average delay was ~119ns with a wider range of delays (standard deviation was 25% greater). > > And, as already stated, I'm failing to find the actual classification > code, but assuming that's RDMSR(s?), how much for them? > As mentioned on patch 1 comments the current patch series doesn't use any classification data produced by the hardware.