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Fri, 15 Nov 2024 04:59:52 +0000 Received: from CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::25a9:32c2:a7b0:de9e]) by CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::25a9:32c2:a7b0:de9e%5]) with mapi id 15.20.8158.013; Fri, 15 Nov 2024 04:59:51 +0000 References: <20241106201758.428310-1-ankur.a.arora@oracle.com> <20241106201758.428310-6-ankur.a.arora@oracle.com> <20241114092225.lVdeX1wG@linutronix.de> User-agent: mu4e 1.4.10; emacs 27.2 From: Ankur Arora To: Sebastian Andrzej Siewior Cc: Ankur Arora , linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de, paulmck@kernel.org, mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, frederic@kernel.org, efault@gmx.de, sshegde@linux.ibm.com, boris.ostrovsky@oracle.com, Daniel Bristot de Oliveira Subject: Re: [PATCH v2 5/6] osnoise: handle quiescent states for PREEMPT_RCU=n, PREEMPTION=y In-reply-to: <20241114092225.lVdeX1wG@linutronix.de> Date: Thu, 14 Nov 2024 20:59:48 -0800 Message-ID: <87sertnlbv.fsf@oracle.com> Content-Type: text/plain X-ClientProxiedBy: MW4PR03CA0312.namprd03.prod.outlook.com (2603:10b6:303:dd::17) To CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) 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: CO6PR10MB5409:EE_|BLAPR10MB4946:EE_ X-MS-Office365-Filtering-Correlation-Id: f8b5a93a-be5e-4b4b-911d-08dd0532568c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024; 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And, for PREEMPT_RCU=y configurations does this >> by directly calling rcu_momentary_eqs(). >> >> With PREEMPT_LAZY=y, however, we can have configurations with >> (PREEMPTION=y, PREEMPT_RCU=n), which means neither of the above >> can help. > > The problem is as you say CONFIG_PREEMPT_RCU=n + CONFIG_PREEMPTION=y. > You can't select any of those two directly but get here via > PREEMPT_LAZY=y + PREEMPT_DYNAMIC=n. > > Please spell it out to make it obvious. It is not a large group of > configurations, it is exactly this combo. Makes sense. Will do. Thanks. Ankur > With PREEMPT_LAZY=y + PREEMPT_DYNAMIC=n however we get PREEMPT_RCU=n > which means no direct rcu_momentary_eqs() invocations and > cond_resched() is an empty stub. > >> Handle that by fallback to the explicit quiescent states via >> rcu_momentary_eqs(). > >> Cc: Paul E. McKenney >> Cc: Daniel Bristot de Oliveira >> Cc: Steven Rostedt >> Suggested-by: Paul E. McKenney >> Acked-by: Daniel Bristot de Oliveira >> Signed-off-by: Ankur Arora > > Sebastian -- ankur