rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config

This commit clarifies that the "p" and the "s" in the in the RCU_NOCB_CPU
config-option description refer to the "x" in the "rcuox/N" kthread name.

Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
[ paulmck: While in the area, update description and advice. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index b71e21f73c40364e3fb78b03a5a30cab22e192ea..cdc57b4f6d48a966d083ec2cb5269fd1b2f5da84 100644 (file)
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -221,19 +221,23 @@ config RCU_NOCB_CPU
          Use this option to reduce OS jitter for aggressive HPC or
          real-time workloads.  It can also be used to offload RCU
          callback invocation to energy-efficient CPUs in battery-powered
-         asymmetric multiprocessors.
+         asymmetric multiprocessors.  The price of this reduced jitter
+         is that the overhead of call_rcu() increases and that some
+         workloads will incur significant increases in context-switch
+         rates.
 
          This option offloads callback invocation from the set of CPUs
          specified at boot time by the rcu_nocbs parameter.  For each
          such CPU, a kthread ("rcuox/N") will be created to invoke
          callbacks, where the "N" is the CPU being offloaded, and where
-         the "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched
-         (!PREEMPTION kernels).  Nothing prevents this kthread from running
-         on the specified CPUs, but (1) the kthreads may be preempted
-         between each callback, and (2) affinity or cgroups can be used
-         to force the kthreads to run on whatever set of CPUs is desired.
-
-         Say Y here if you want to help to debug reduced OS jitter.
+         the "x" is "p" for RCU-preempt (PREEMPTION kernels) and "s" for
+         RCU-sched (!PREEMPTION kernels).  Nothing prevents this kthread
+         from running on the specified CPUs, but (1) the kthreads may be
+         preempted between each callback, and (2) affinity or cgroups can
+         be used to force the kthreads to run on whatever set of CPUs is
+         desired.
+
+         Say Y here if you need reduced OS jitter, despite added overhead.
          Say N here if you are unsure.
 
 config TASKS_TRACE_RCU_READ_MB