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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 Subject: Re: [RFC PATCH v4 3/4] hazptr: Implement Hazard Pointers Message-ID: References: <20251218014531.3793471-1-mathieu.desnoyers@efficios.com> <20251218014531.3793471-4-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E832E140006 X-Stat-Signature: kcrdpo987kebyf359wswb6brh8cm7omo X-HE-Tag: 1766105025-911238 X-HE-Meta: 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 6t1Gcty4 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Dec 18, 2025 at 12:35:18PM -0500, Mathieu Desnoyers wrote: [...] > > Could you utilize this[1] to see a > > comparison of the reader-side performance against RCU/SRCU? > > Good point ! Let's see. > > On a AMD 2x EPYC 9654 96-Core Processor with 192 cores, > hyperthreading disabled, > CONFIG_PREEMPT=y, > CONFIG_PREEMPT_RCU=y, > CONFIG_PREEMPT_HAZPTR=y. > > scale_type ns > ----------------------- > hazptr-smp-mb 13.1 <- this implementation > hazptr-barrier 11.5 <- replace smp_mb() on acquire with barrier(), requires IPIs on synchronize. > hazptr-smp-mb-hlist 12.7 <- replace per-task hp context and per-cpu overflow lists by hlist. > rcu 17.0 Hmm.. now looking back, how is it possible that hazptr is faster than RCU on the reader-side? Because a grace period was happening and triggered rcu_read_unlock_special()? This is actualy more interesting. Regards, Boqun > srcu 20.0 > srcu-fast 1.5 > rcu-tasks 0.0 > rcu-trace 1.7 > refcnt 1148.0 > rwlock 1190.0 > rwsem 4199.3 > lock 41070.6 > lock-irq 46176.3 > acqrel 1.1 > > So only srcu-fast, rcu-tasks, rcu-trace and a plain acqrel > appear to beat hazptr read-side performance. > > [...] > [...]