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We have to wait for > SET_AFFINITY_CHECK_PERIOD_MASK grace periods before the affinity is set > (it takes about 2.5s in my benchmarks). > > This means that short-lived test programs will get poor CPU affinity > for call-rcu worker threads at the beginning of their lifetime. So for > short lived programs, this means poor performance. > > OTOH, if we have short-lived applications on a large machine, setting > the affinity immediately when the worker thread is starting means > we use CPU time on CPUs which may never be actually used by the > application (no call-rcu activity), which can be detrimental to other > use-cases as well. > > So I was wondering: is the choice of skipping setting the affinity > on call-rcu worker thread startup done on purpose ? And if so, > should we perhaps consider setting the affinity as soon as the > worker thread is woken up for the first time rather than after > SET_AFFINITY_CHECK_PERIOD_MASK grace periods ? I've implemented this compromise approach here: https://review.lttng.org/c/userspace-rcu/+/18257 call-rcu worker: set CPU affinity on first non-empty dequeue Feedback is welcome, Thanks! Mathieu > > Note that there is a commit in liburcu changing this behavior right > now, but it's not part of any release yet. I want to figure out the > wanted behavior before releasing this change: > > commit 28f282af1905a1cf50ff9b5835b4cd9de4416ddf > Author: Mathieu Desnoyers > Date:   Wed Jul 1 12:49:43 2026 -0400 > >     call_rcu: pin per-CPU worker at thread startup > > Thanks, > > Mathieu > -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com