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charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: btaexwfzxdw3hfqtj7x8wxzjkejts3ow X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6F5CF1A000F X-HE-Tag: 1771406961-648024 X-HE-Meta: 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 rnhzzVqC CPu+GwKWhjJgUSgTydXjd6i/RrC07x///F7WZk74K2sSKSeZekidFC6gSqvFf8bO0MQYhk585+AUG6EQk17NbKHswVNsUXHZXN0evBKx0fvM3TzUefSln93IcZGBAar0Cp3w2nVXtlzpTXehBjpU0jNmWlLc7FfIbgc/y560ZTNR+8PooZSjD/aJK9PTiTlR5PPSdLdBBGeR+O6hLVenhi43ZgA== 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: Hi Prateek, On Wed, Feb 18, 2026 at 09:31:19AM +0530, K Prateek Nayak wrote: > On 2/17/2026 10:18 PM, Catalin Marinas wrote: > > Yes, that would be good. It's the preempt_enable_notrace() path that > > ends up calling preempt_schedule_notrace() -> __schedule() pretty much > > unconditionally. > > What do you mean by unconditionally? We always check > __preempt_count_dec_and_test() before calling into __schedule(). > > On x86, We use MSB of preempt_count to indicate a resched and > set_preempt_need_resched() would just clear this MSB. > > If the preempt_count() turns 0, we immediately go into schedule > or or the next preempt_enable() -> __preempt_count_dec_and_test() > would see the entire preempt_count being clear and will call into > schedule. > > The arm64 implementation seems to be doing something similar too > with a separate "ti->preempt.need_resched" bit which is part of > the "ti->preempt_count"'s union so it isn't really unconditional. Ah, yes, you are right. I got the polarity of need_resched in thread_info wrong (we should have named it no_need_to_resched). So in the common case, the overhead is caused by the additional pointer chase and preempt_count update, on top of the cpu offset read. Not sure we can squeeze any more cycles out of these without some large overhaul like: https://git.kernel.org/mark/c/84ee5f23f93d4a650e828f831da9ed29c54623c5 or Yang's per-CPU page tables. Well, there are more ideas like in-kernel restartable sequences but they move the overhead elsewhere. Thanks. -- Catalin