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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/23/26 1:50 AM, Heiko Carstens wrote: > On Wed, Feb 11, 2026 at 03:14:57PM -0800, Yang Shi wrote: >> Design >> ====== >> To improve the performance for this_cpu_ops on ARM64 and potentially >> some other non-x86 architectures, I and Christopher Lameter proposed >> the below solution. > ... > >> I have done some PoC on ARM64. Hopefully I can post them to the >> mailing list to ease the discussion before the conference. > FWIW, from an s390 perspective we have been relying on that preempt_disable() > and preempt_enable() pairs for this_cpu*() ops are optimized away at compile > time for PREEMPT_NONE and PREEMPT_VOLUNTARY. Which is what all distributions > did, until now. > > With 7dadeaa6e851 ("sched: Further restrict the preemption modes") this is not > the case anymore. So the overhead will be there for every "up-to-date" > architecture except x86. I've been looking at some ways how to get rid of this > extra overhead for s390. E.g. we have an "access register mode", which can be > sort of compared to the x86 segment register approach, but switching the CPU > to this mode and back is more expensive than the preempt_disable() and > preempt_enable() pairs. If I read the code correctly, preempt_disable/enable are *NOT* no-op on arm64 even though PREEMPT_VOLUNTARY is enabled. I tested with CONFIG_PREEMPT (should be called PREEMPT_FULL before), I saw roughly 2% more real time improvement on kernel build workload comparing to PREEMPT_VOLUNTARY. The improvement for sys time basically stays same. > > To make the long story short: I'm very interested in your approch from an s390 > perspective (aka "other non-x86 architectures"). Thanks for showing interest. Hopefully I can cleanup the patches, then post them to the mailing list before LSF/MM so that people can test it on other architectures, for example, s390. But it may still have a lot hack and ad hoc code. Thanks, Yang