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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> <20241115101100.GZ22801@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241115101100.GZ22801@noisy.programming.kicks-ass.net> X-ClientProxiedBy: MA0PR01CA0019.INDPRD01.PROD.OUTLOOK.COM (2603:1096:a01:b8::6) 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_|CH3PR12MB8460:EE_ X-MS-Office365-Filtering-Correlation-Id: f7b0100b-85bd-4476-7dec-08dd0d147016 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7416014; 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I was away most of last week. On Fri, Nov 15, 2024 at 11:11:00AM +0100, Peter Zijlstra wrote: [..snip..] > > > > > But if it were to use MWAIT for regular idle, then surely it's OK for > > > offline too, right? Yes, this is not a problem. > > > > 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. > > Right, but in most cases you'll have C2/C3 with io ports specified and > those will be picked for play_dead anyway. It's just the exceptionally > weird BIOS case where you'll have C2/C3 as FFh -- because random BIOS > person was on drugs that day or something like that. It is unlikely to have a BIOSes on AMD platforms that allow users to disable ACPI C2 state. That would be the only scenario when an offlined CPU would enter FFH based C1. > > Anyway, what I'm trying to say is that you'll probably fine without > adding a bunch of if (AMD|HYGON) logic -- the less of that we have, the > better, etc.. I agree, I will resend the patch without this check. -- Thanks and Regards gautham.