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I'm staring at this now, and I'm thinking we could do a simpler change that would solve your RT issues without having to introduce a dependency on workqueue.c. So if the culprit is that task_mm_cid_work() runs for too long on large many-cpus systems, why not break it up into smaller iterations ? So rather than iterating on "for_each_possible_cpu", we could simply break this down into iteration on at most N cpus, so: tick #1: iteration on CPUs 0 .. N - 1 tick #2: iteration on CPUs N .. 2*N - 1 ... circling back to 0 when it reaches the number of possible cpus. This N value could be configurable, e.g. CONFIG_RSEQ_CID_SCAN_BATCH, with a sane default. An RT system could decide to make that value lower. Then all we need to do is remember which was that last observed cpu number in the mm struct, so the next tick picks up from there. The main downside of this approach compared to scheduling delayed work in a workqueue is that it depends on having the mm be current when the scheduler tick happens. But perhaps this is something we could fix in a different way that does not add a dependency on workqueue. I'm not sure how though. Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com