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CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) by SJ0PR10MB5803.namprd10.prod.outlook.com (2603:10b6:a03:427::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7362.36; Tue, 12 Mar 2024 03:15:40 +0000 Received: from CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::4104:529:ba06:fcb8]) by CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::4104:529:ba06:fcb8%7]) with mapi id 15.20.7362.035; Tue, 12 Mar 2024 03:15:40 +0000 References: <20240213055554.1802415-1-ankur.a.arora@oracle.com> <20240213055554.1802415-16-ankur.a.arora@oracle.com> <20240310100330.GA2705505@joelbox2> <87r0ghl51f.fsf@oracle.com> <66820daa-421b-469a-a7e8-ae7ae9dfa978@joelfernandes.org> <87wmq8pop1.ffs@tglx> <5b78a338-cb82-4ac4-8004-77a3eb150604@joelfernandes.org> User-agent: mu4e 1.4.10; emacs 27.2 From: Ankur Arora To: Joel Fernandes Cc: Thomas Gleixner , Ankur Arora , paulmck@kernel.org, linux-kernel@vger.kernel.org, peterz@infradead.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jpoimboe@kernel.org, mark.rutland@arm.com, jgross@suse.com, andrew.cooper3@citrix.com, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, rcu@vger.kernel.org Subject: Re: [PATCH 15/30] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y In-reply-to: <5b78a338-cb82-4ac4-8004-77a3eb150604@joelfernandes.org> Date: Mon, 11 Mar 2024 20:16:12 -0700 Message-ID: <87msr4f8cj.fsf@oracle.com> Content-Type: text/plain 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9RWi8GXA2qZYevKGBXSInQLiXx-G4rVR Joel Fernandes writes: > Hi, Thomas, > Thanks for your reply! I replied below. > > On 3/11/2024 3:12 PM, Thomas Gleixner wrote: >> On Mon, Mar 11 2024 at 11:25, Joel Fernandes wrote: [ ... ] >> What's wrong with the combination of PREEMPT_AUTO=y and PREEMPT_RCU=n? >> Paul and me agreed long ago that this needs to be supported. > > There's nothing wrong with it. Its just a bit quirky (again just a point of > view), that for a configuration that causes preemption (similar to > CONFIG_PREEMPT=y), that PREEMPT_RCU can be disabled. After all, again with > CONFIG_PREEMPT=y, PREEMPT_RCU cannot be currently disabled. I think the argument was that PREEMPT_RCU=y is suboptimal for certain workloads, and those configurations might prefer the stronger forward-progress guarantees that PREEMPT_RCU=n provides. See this: https://lore.kernel.org/lkml/73ecce1c-d321-4579-b892-13b1e0a0620a@paulmck-laptop/T/#m6aab5a6fd5f1fd4c3dc9282ce564e64f2fa6cdc3 and the surrounding thread. Thanks -- ankur