[PATCH 0/5] handle kthread_prio kernel cmdline parameter consistently

[Alison Chaiken]

When CONFIG_PREEMPT_RT=y, RCU_SOFTIRQ work is moved to dedicated rcuc
per-core threads.  The rcutree.kthread_prio kernel cmdline parameter
controls the priority of those threads.

A provided kthread_prio kernel cmdline parameter also elevates the
priority of rcuog threads, but only if they are launched from
rcu_spawn_gp_kthread(), not if they are launched from
rcu_spawn_one_nocb_kthread().  Fix this inconsistency.

When CONFIG_RCU_NOCB_CPU=y, an rcu_nocbs command-line parameter
offloads the work of rcuc on designated cores to new rcuop threads
that are not pinned to the cores whose expired grace-period timer
callbacks they run.  While rcuop threads have the same function as
rcuc threads, their priority is not controlled by the kthread_prio
parameter.  Add this feature and update the documentation accordingly.

Alison Chaiken (4):
  RCU: move kthread_prio bounds-check to a separate function
  RCU: make priority of grace-period thread consistent
  RCU: elevate priority of offloaded callback threads
  RCU: update documentation regarding kthread_prio cmdline parameter

 .../admin-guide/kernel-parameters.txt         |  2 +
 kernel/rcu/tree.c                             | 42 +++++++++++--------
 kernel/rcu/tree_nocb.h                        |  7 ++++
 3 files changed, 34 insertions(+), 17 deletions(-)

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2.32.0