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McKenney" , linux-kernel@vger.kernel.org, Nicholas Piggin , Michael Ellerman , Greg Kroah-Hartman , Sebastian Andrzej Siewior , Will Deacon , Peter Zijlstra , Alan Stern , John Stultz , Neeraj Upadhyay , Linus Torvalds , Andrew Morton , Frederic Weisbecker , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Lai Jiangshan , Zqiang , Ingo Molnar , Waiman Long , Mark Rutland , Thomas Gleixner , Vlastimil Babka , maged.michael@gmail.com, Mateusz Guzik , Jonas Oberhauser , rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev References: <20251218014531.3793471-1-mathieu.desnoyers@efficios.com> <20251218014531.3793471-5-mathieu.desnoyers@efficios.com> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: YQBPR0101CA0279.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:68::10) To YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:be::5) 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: YT2PR01MB9175:EE_|YT2PR01MB10504:EE_ X-MS-Office365-Filtering-Correlation-Id: 7bb88b4d-4e50-4616-40af-08de3e948f05 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014; 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Removing the PREEMPT_HAZPTR brings read-side performance from 13.1 down to 5.1 ns. So there is a surprising amount of work that goes into list_add/list_del. I just noticed that I was running a kernel with CONFIG_LIST_HARDENED=y. Reruning refscale for PREEMPT_HAZPTR=y with list hardening disabled goes from 13.1 ns to 12.4ns, so not a huge win. I did not notice much difference in terms of scheduler performance with a quick hackbench run, but I cannot claim it is an extensive benchmark in any way. > > I think you need to add interrupt disabling for chain/unchain because of > the potential readers in interrupt and then you can avoid the preempt > disabling in hazptr_release() I think. Let's aim for supporting readers > in interrupt handler, because at least lockdep needs that. OK, I'll look into it! Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com