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Wed, 11 Feb 2026 15:39:02 -0800 (PST) Date: Wed, 11 Feb 2026 15:39:02 -0800 (PST) From: "Christoph Lameter (Ampere)" To: Tejun Heo 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) In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam12 X-Stat-Signature: ugjisyihunco3occo5hphao5j9on5wfi X-Rspamd-Queue-Id: 5BFD8180006 X-Rspam-User: X-HE-Tag: 1770853144-453258 X-HE-Meta: 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 L6DMwB/i FV2FZYFOm3WIx4c9DyHWvbefX22KWPXKR+uRlThWOuZjuIQho4skgDq0in7b6bI1KXmZLVi/jHEGcVpI4TQO2vuOOy6V9qi7hcQfnCGoKjG7nLo/njOTfePRX4p8GDqIHfeyxuvJmgR3Ku9BD/wwa4AEHivNZu86/0m688b46qzwA6QN2jkLOXjPjnV+J15w8Pq5sBpBVyOjptqUhelr6zIPGb4xBLoXcy58g8vDF0wgtqbhXpuWxsKKatr3eeZhaIWApY9aSZS70COU4dpxBBMxxOFuNQNnIvnyuHna7uArFJuFNtvgGemmZNOHvUSdR5cOv 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, 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. 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. > Generally sounds like a great solution for !x86. Thanks.