Hello all, On 6.1.71-rt21 (PREEMPT_RT against vanilla) I am trying to find the root cause of an "rcuc" thread scheduled in on an isolated core (CPU #4). The isolated core should run a single non-kernel user-space-busy-loop thread (SCHED_OTHER, not FIFO or RR). tsc=reliable isolcpus=domain,managed_irq,4-7 nohz_full=4-7 rcu_nocbs=all rcu_nocb_poll /proc/irq/*/smp_affinity and cpumasks in /sys/devices/virtual/workqueue/ all show 000f or less (CPUs 0-3) Using osnoise I see rcuc/4 popping up as a cause of noise, but my kernel command line should prevent that, right? I see this in the kernel boot log, and I wonder if this is related to my issue: [ 0.063518] rcu: RCU_SOFTIRQ processing moved to rcuc kthreads. tree.c:102:static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT); Could this cause the rcuc threads to become active, even with the "rcu_nocbs=all rcu_nocb_poll" setting? Thanks, Leon. [ 0.063516] rcu: Preemptible hierarchical RCU implementation. [ 0.063517] rcu: RCU restricting CPUs from NR_CPUS=8192 to nr_cpu_ids=16. [ 0.063518] rcu: RCU priority boosting: priority 1 delay 500 ms. [ 0.063518] rcu: RCU_SOFTIRQ processing moved to rcuc kthreads. [ 0.063519] No expedited grace period (rcu_normal_after_boot). [ 0.063519] Trampoline variant of Tasks RCU enabled. [ 0.063519] Rude variant of Tasks RCU enabled. [ 0.063520] Tracing variant of Tasks RCU enabled. [ 0.063520] rcu: RCU calculated value of scheduler-enlistment delay is 25 jiffies. [ 0.063521] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=16 [ 0.066896] NO_HZ: Full dynticks CPUs: 4-7. [ 0.066897] rcu: Offload RCU callbacks from CPUs: 0-15. [ 0.066898] rcu: Poll for callbacks from no-CBs CPUs. [ 0.066901] rcu: srcu_init: Setting srcu_struct sizes based on contention. [ 1.145094] rcu: Hierarchical SRCU implementation. [ 1.145094] rcu: Max phase no-delay instances is 1000. -- Leon Woestenberg leon@xxxxxxxxxxxxxx T: +31 40 711 42 76 M: +31 6 472 30 372 Sidebranch Embedded Systems Eindhoven, The Netherlands http://www.sidebranch.com
