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[209.85.208.52]) by smtp.gmail.com with ESMTPSA id j24sm231216edp.44.2021.07.28.11.40.30 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Jul 2021 11:40:30 -0700 (PDT) Received: by mail-ed1-f52.google.com with SMTP id da26so4607308edb.1 for ; Wed, 28 Jul 2021 11:40:30 -0700 (PDT) X-Received: by 2002:a2e:9241:: with SMTP id v1mr660028ljg.48.1627497136138; Wed, 28 Jul 2021 11:32:16 -0700 (PDT) MIME-Version: 1.0 References: <20210721202042.GA1472052@paulmck-ThinkPad-P17-Gen-1> <20210721202127.2129660-4-paulmck@kernel.org> <20210728173715.GA9416@paulmck-ThinkPad-P17-Gen-1> <1810346528.8990.1627495925037.JavaMail.zimbra@efficios.com> In-Reply-To: <1810346528.8990.1627495925037.JavaMail.zimbra@efficios.com> From: Linus Torvalds Date: Wed, 28 Jul 2021 11:32:00 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 rcu 04/18] rcu: Weaken ->dynticks accesses and updates To: Mathieu Desnoyers Cc: paulmck , rcu , linux-kernel , kernel-team , Ingo Molnar , Lai Jiangshan , Andrew Morton , Josh Triplett , Thomas Gleixner , Peter Zijlstra , rostedt , David Howells , Eric Dumazet , fweisbec , Oleg Nesterov , "Joel Fernandes, Google" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 28, 2021 at 11:12 AM Mathieu Desnoyers wrote: > > Are the percpu atomics you have in mind different from what is found in > Documentation/core-api/this_cpu_ops.rst ? > > Namely this_cpu_add_return(pcp, val) in this case. Nope. Those are only "CPU-atomic", ie atomic wrt interrupts etc. The RCU code wants SMP-atomic, and it's mainly that we *could* do the addressing more efficiently. Linus