rcu: priority boosting for TINY_PREEMPT_RCU

Add priority boosting, but only for TINY_PREEMPT_RCU.  This is enabled
by the default-off RCU_BOOST kernel parameter.  The priority to which to
boost preempted RCU readers is controlled by the RCU_BOOST_PRIO kernel
parameter (defaulting to real-time priority 1) and the time to wait
before boosting the readers blocking a given grace period is controlled
by the RCU_BOOST_DELAY kernel parameter (defaulting to 500 milliseconds).

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index a619a1ac7f4c..48efefcac12a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -450,6 +450,45 @@ config TREE_RCU_TRACE
           TREE_PREEMPT_RCU implementations, permitting Makefile to
           trivially select kernel/rcutree_trace.c.
 
+config RCU_BOOST
+        bool "Enable RCU priority boosting"
+        depends on RT_MUTEXES && TINY_PREEMPT_RCU
+        default n
+        help
+          This option boosts the priority of preempted RCU readers that
+          block the current preemptible RCU grace period for too long.
+          This option also prevents heavy loads from blocking RCU
+          callback invocation for all flavors of RCU.
+
+          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"
+        range 1 99
+        depends on RCU_BOOST
+        default 1
+        help
+          This option specifies the real-time priority to which preempted
+          RCU readers are to be boosted.  If you are working with CPU-bound
+          real-time applications, you should specify a priority higher then
+          the highest-priority CPU-bound application.
+
+          Specify the real-time priority, or take the default if unsure.
+
+config RCU_BOOST_DELAY
+        int "Milliseconds to delay boosting after RCU grace-period start"
+        range 0 3000
+        depends on RCU_BOOST
+        default 500
+        help
+          This option specifies the time to wait after the beginning of
+          a given grace period before priority-boosting preempted RCU
+          readers blocking that grace period.  Note that any RCU reader
+          blocking an expedited RCU grace period is boosted immediately.
+
+          Accept the default if unsure.
+
 endmenu # "RCU Subsystem"
 
 config IKCONFIG