From: Leon Woestenberg <leon@sidebranch.com>
To: linux-rt-users@vger.kernel.org
Subject: Unexpected rcuc osnoise on PREEMPT_RT with "rcu_nocbs=all rcu_nocb_poll"
Date: Fri, 19 Jan 2024 16:38:23 +0100 [thread overview]
Message-ID: <CAMjhiJj0PnBrZdujKWnF43TmLB37L-bfs99nyDi+j2p+Nv1enQ@mail.gmail.com> (raw)
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@sidebranch.com
T: +31 40 711 42 76
M: +31 6 472 30 372
Sidebranch Embedded Systems
Eindhoven, The Netherlands
http://www.sidebranch.com
next reply other threads:[~2024-01-19 15:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-19 15:38 Leon Woestenberg [this message]
2024-01-19 22:08 ` Unexpected rcuc osnoise on PREEMPT_RT with "rcu_nocbs=all rcu_nocb_poll" Frederic Weisbecker
2024-01-20 0:37 ` Paul E. McKenney
2024-01-22 14:32 ` Leon Woestenberg
2024-01-23 18:32 ` Paul E. McKenney
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