Le Fri, Jan 19, 2024 at 04:38:23PM +0100, Leon Woestenberg a écrit : > 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? That's unexpected. The RCU load should be moved from rcuc to rcuo* kthreads. Do you have CONFIG_RCU_STRICT_GRACE_PERIOD=y perhaps? Also do you really need rcu_nocb_poll? I would expect this option to be useful for debugging only, though I'm not aware of every usecases. Thanks. > > > 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 >
