rcu: Unify boost and kthread priorities

Rename CONFIG_RCU_BOOST_PRIO to CONFIG_RCU_KTHREAD_PRIO and use this
value for both the per-CPU kthreads (rcuc/N) and the rcu boosting
threads (rcub/n).

Also, create the module_parameter rcutree.kthread_prio to be used on
the kernel command line at boot to set a new value (rcutree.kthread_prio=N).

Signed-off-by: Clark Williams <clark.williams@gmail.com>
[ paulmck: Ported to rcu/dev, applied Paul Bolle and Peter Zijlstra feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 12 insertions, 11 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 0c9546ba56e8..15c299cc7c1e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -672,30 +672,31 @@ config RCU_BOOST
           Say Y here if you are working with real-time apps or heavy loads
           Say N here if you are unsure.
 
-config RCU_BOOST_PRIO
-        int "Real-time priority to boost RCU readers to"
+config RCU_KTHREAD_PRIO
+        int "Real-time priority to use for RCU worker threads"
         range 1 99
         depends on RCU_BOOST
         default 1
         help
-          This option specifies the real-time priority to which long-term
-          preempted RCU readers are to be boosted.  If you are working
-          with a real-time application that has one or more CPU-bound
-          threads running at a real-time priority level, you should set
-          RCU_BOOST_PRIO to a priority higher then the highest-priority
-          real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
-          of 1 is appropriate in the common case, which is real-time
+          This option specifies the SCHED_FIFO priority value that will be
+          assigned to the rcuc/n and rcub/n threads and is also the value
+          used for RCU_BOOST (if enabled). If you are working with a
+          real-time application that has one or more CPU-bound threads
+          running at a real-time priority level, you should set
+          RCU_KTHREAD_PRIO to a priority higher than the highest-priority
+          real-time CPU-bound application thread.  The default RCU_KTHREAD_PRIO
+          value of 1 is appropriate in the common case, which is real-time
           applications that do not have any CPU-bound threads.
 
           Some real-time applications might not have a single real-time
           thread that saturates a given CPU, but instead might have
           multiple real-time threads that, taken together, fully utilize
-          that CPU.  In this case, you should set RCU_BOOST_PRIO to
+          that CPU.  In this case, you should set RCU_KTHREAD_PRIO to
           a priority higher than the lowest-priority thread that is
           conspiring to prevent the CPU from running any non-real-time
           tasks.  For example, if one thread at priority 10 and another
           thread at priority 5 are between themselves fully consuming
-          the CPU time on a given CPU, then RCU_BOOST_PRIO should be
+          the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
           set to priority 6 or higher.
 
           Specify the real-time priority, or take the default if unsure.