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Fri, 25 Oct 2024 12:30:32 -0700 (PDT) Date: Fri, 25 Oct 2024 12:30:32 -0700 (PDT) From: "Christoph Lameter (Ampere)" To: Peter Zijlstra cc: Linus Torvalds , Will Deacon , Thomas Gleixner , Catalin Marinas , Ingo Molnar , Waiman Long , Boqun Feng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org Subject: Re: [PATCH v3] Avoid memory barrier in read_seqcount() through load acquire In-Reply-To: <20241025074244.GB14555@noisy.programming.kicks-ass.net> Message-ID: <797cf697-83b2-7f45-4865-2ee394887dc8@gentwo.org> References: <20240912-seq_optimize-v3-1-8ee25e04dffa@gentwo.org> <20240917071246.GA27290@willie-the-truck> <4b546151-d5e1-22a3-a6d5-167a82c5724d@gentwo.org> <20241023194543.GD11151@noisy.programming.kicks-ass.net> <20241025074244.GB14555@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspam-User: X-Stat-Signature: kaoc7kp9hsgu7iw8syt7tus1omzcm73o X-Rspamd-Queue-Id: 1805E40009 X-Rspamd-Server: rspam11 X-HE-Tag: 1729888855-813584 X-HE-Meta: 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 uzvpOVDu LooZgtm3VFGPEa1zv09EfJoKtXS443OW0+EyfvuR2lV1wCeDapEKfnDy7ObTloXNe/wS5mdyXouOAS6gvsgL439j8nkwYOZr2MUU1cQEwtnGylQ7Oqk1g3kK2uLFBX9OcjPukntSFgRsBALqPFJF2rHJERXJE3K1etnYuQGtA2FBN/29XEU8HGPs72hI/lxgHw3168YnhD7nH7OjY3tTwVO2GavHzq0vOIOFGsbJ4WhSu0uSmH9UZ5ZMlQz5OBUuXXvt3s7OMB6ygVfXWzPJIAtz4e2HcKXYtjZmtXxJ1FpiL2N3ROMjrbzH2Pe8RGIQPVLz5 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 Fri, 25 Oct 2024, Peter Zijlstra wrote: > > atomic_inc_release(&seqcount) > > It would not be, making the increment itself atomic would make the whole > thing far more expensive. True. I was too much taken by a cool hw feature on ARM.