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b=uLwxXdL8F75bnDK5USEl0ETGj9zSOoN7uGEgp4FC7xJTnT7E8Ecyey83lvNriU1OC b7NCLRIBXrh65b0/hCAnmubR2qXUuQ5tlN+dqV0ELE8P/iPRUGMj4uvsYwQjsLLVxf iwKJck7IC5sPKUWYOTJSzGuXgbXqyZFwkGdsWb7QpHJ3wC8l/m8e5dQaI41BnxgweZ SS49kiOSb9yM8BCSaZy5Kv3zJsr0SVM/49pkCPhAq0bDfZGsSHVQb4hSr+tt85R2ZJ bhnETEY/r1SQSQLfp7jLW+aAl1snYPoaNwQ/LzQcdUDMi7qcvmW0uSfwmjUqnj4J1H ZpD/vhXDOZ8pQ== Date: Wed, 11 Feb 2026 13:40:24 -1000 From: Tejun Heo To: "Christoph Lameter (Ampere)" Cc: Yang Shi , lsf-pc@lists.linux-foundation.org, Linux MM , dennis@kernel.org, urezki@gmail.com, Catalin Marinas , Will Deacon , Ryan Roberts , Yang Shi Subject: Re: [LSF/MM/BPF TOPIC] Improve this_cpu_ops performance for ARM64 (and potentially other architectures) Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: za4xs533u66akg6ymk4itpwg6sisi7au X-Rspamd-Queue-Id: 22E2910000F X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770853226-950828 X-HE-Meta: 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 7cyC1Ysg auvvXBK5XK9L9Ca7E0Ptg4yaTkp3q/UDYPwhSS3tVXsrtgbJOKHsRAbwvXr9f2im7anoQisrxT1250kanlZpQ9kzsI1W9X+HbuZqflZx6CTJVeuz1ZEPksAmAVO95X+R3T69Q0Z7M39s2e7VrqR3nWTuXxINCoABQxIkjLPT0XDBBQ/64Vx3ZCbuWjgGMaTqBDiWUU+XkicxCX96yJ3o8c8i/wYJP7ARIquCj+oUJKbCnhftRzQ7pxYZcHyDCfdl6+dd8EJMQQH2ZIw/fhqGZsLTtpiL1XaOy7DbT 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 Wed, Feb 11, 2026 at 03:39:02PM -0800, Christoph Lameter (Ampere) wrote: > On Wed, 11 Feb 2026, Tejun Heo wrote: > > > One property that this breaks is per_cpu_ptr() of a given CPU disagreeing > > with this_cpu_ptr(). e.g. If there are users that take this_cpu_ptr() and > > uses that outside preempt disable block (which is a bit odd but allowed), > > this_cpu_ptr converts a percpu variable offset to a normal pointer that > can be used without preemption. Ah, no problem then. > If the scheduler changes the cpu then you would remotely access that per > cpu data in a remote cpu. Read only acces is fine. Writing could be dicey > in some cases. Yeah, that's the current behavior. Thanks. -- tejun