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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Mathieu Desnoyers via lttng-dev Reply-To: Mathieu Desnoyers Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" Hi Paul, I have a question related to liburcu per-cpu call-rcu worker threads. So far in the current liburcu releases no affinity is set when the worker threads are started. 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 ? 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