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Tue, 17 Feb 2026 09:19:22 -0800 (PST) Date: Tue, 17 Feb 2026 09:19:22 -0800 (PST) From: "Christoph Lameter (Ampere)" To: Dev Jain cc: Will Deacon , Jisheng Zhang , Catalin Marinas , Dennis Zhou , Tejun Heo , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, maz@kernel.org Subject: Re: [PATCH] arm64: remove HAVE_CMPXCHG_LOCAL In-Reply-To: <89606308-3c03-4dcf-a89d-479258b710e4@arm.com> Message-ID: <6d30176d-9673-287e-4658-a5e9e6e5d649@gentwo.org> References: <20260215033944.16374-1-jszhang@kernel.org> <89606308-3c03-4dcf-a89d-479258b710e4@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: cugu69jyonrbw84fxtsurhbtfd9m1n3e X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 4A454180004 X-HE-Tag: 1771348764-77045 X-HE-Meta: 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 hQFupc0q R2zW6xBdMKolydsf0j6JSzT+Z9627KR22fDOE6psRyUFj6l2P9wTL9iFQuuixudWMCLgwoDy+bkL3d2jorejnOic/oXr63Vin2GTqP8rbA4hCkEukGBDCZS6hQZ0D8h3cLYqdqusb1D2Rad07iz6JRjx5mijXx2XSIe/7gEU7NgnLqrbU2zzjEVeuWVGOlPpWPDUNmQmGY0meuW0i+W3HIAc6V/IhrJh11nghCaDngUPiEkqt/2f4YjlNLeieJ+Bu4BR3d31eHLHwT3B5apbA/8f5KAySDpFr2b1X68XXi3hjC2k= 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 Mon, 16 Feb 2026, Dev Jain wrote: > By coincidence, Yang Shi has been discussing the this_cpu_* overhead > at [2]. Yang Shi is on vacation but we have a patchset that removes preempt_enable/disable from this_cpu operations on ARM64. The performance of cmpxchg varies by platform in use and with the kernel config. The measurements that I did 2 years ago indicated that the cmpxchg use with Ampere processors did not cause a regression. Note that distro kernels often do not enable PREEMPT_FULL and therefore preempt_disable/enable overhead is not incurred in production systems. PREEMPT_VOLUNTARY does not use preemption for this_cpu ops.