On 2025-03-10 10:46, Gabriele Monaco wrote:
On Thu, 2025-02-27 at 16:33 +0100, Gabriele Monaco wrote:Currently, the task_mm_cid_work function is called in a task work triggered by a scheduler tick to frequently compact the mm_cids of each process. This can delay the execution of the corresponding thread for the entire duration of the function, negatively affecting the response in case of real time tasks. In practice, we observe task_mm_cid_work increasing the latency of 30-35us on a 128 cores system, this order of magnitude is meaningful under PREEMPT_RT. Run the task_mm_cid_work in a new work_struct connected to the mm_struct rather than in the task context before returning to userspace. This work_struct is initialised with the mm and disabled before freeing it. The queuing of the work happens while returning to userspace in __rseq_handle_notify_resume, maintaining the checks to avoid running more frequently than MM_CID_SCAN_DELAY. To make sure this happens predictably also on long running tasks, we trigger a call to __rseq_handle_notify_resume also from the scheduler tick if the runtime exceeded a 100ms threshold. [...] Fixes: 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid") Signed-off-by: Gabriele Monaco <gmonaco@xxxxxxxxxx>Is this patch missing anything? I refactored a bit to have it build in configurations without RSEQ and/or MM_CID (which was failing v10)
Found a small nit. Please fix and resend with my reviewed-by, and that version will be ready for inclusion. Thanks! Mathieu
Thanks, Gabriele
-- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com
