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Shenoy" To: Peter Zijlstra Cc: "Rafael J. Wysocki" , Patryk Wlazlyn , x86@kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, rafael.j.wysocki@intel.com, len.brown@intel.com, artem.bityutskiy@linux.intel.com, dave.hansen@linux.intel.com, Mario Limonciello Subject: Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play_dead() Message-ID: References: <20241108122909.763663-1-patryk.wlazlyn@linux.intel.com> <20241108122909.763663-3-patryk.wlazlyn@linux.intel.com> <20241112114743.GQ22801@noisy.programming.kicks-ass.net> <20241112145618.GR22801@noisy.programming.kicks-ass.net> <20241114115831.GQ6497@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241114115831.GQ6497@noisy.programming.kicks-ass.net> X-ClientProxiedBy: PNYP287CA0014.INDP287.PROD.OUTLOOK.COM (2603:1096:c01:23d::18) To DS7PR12MB8252.namprd12.prod.outlook.com (2603:10b6:8:ee::7) Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB8252:EE_|DS7PR12MB6216:EE_ X-MS-Office365-Filtering-Correlation-Id: ecdc120e-0ebf-46cf-e05e-08dd04d12f1f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016; 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Shenoy wrote: > > > AMD platforms won't be using FFH based states for offlined CPUs. We > > prefer IO based states when available, and HLT otherwise. > > > > > > > > Robustly we'd teach the ACPI driver about FFh and set enter_dead on > > > every state -- but we'd have to double check that with AMD. > > > > Works for us as long as those FFh states aren't used for play_dead on > > AMD platforms. > > AFAIU AMD doesn't want to use MWAIT -- ever, not only for offline. > Confirm? > AMD wants to use MWAIT for cpuidle and it does use MWAIT based C1 state on both client and server parts. Eg: On my server box $ cpupower idle-info | grep "FFH" -B1 -A3 C1: Flags/Description: ACPI FFH MWAIT 0x0 Latency: 1 Usage: 6591 Duration: 1482606 > But if it were to use MWAIT for regular idle, then surely it's OK for > offline too, right? I tried this out today and there is no functional issue. However, I would like to run some experiments on whether HLT provides better power savings than MWAIT C1 with CPUs offlined. I will get back with this information tomorrow. -- Thanks and Regards gautham.