rcu: Add rcutorture CPU-hotplug capability

Running CPU-hotplug operations concurrently with rcutorture has
historically been a good way to find bugs in both RCU and CPU hotplug.
This commit therefore adds an rcutorture module parameter called
"onoff_interval" that causes a randomly selected CPU-hotplug operation to
be executed at the specified interval, in seconds.  The default value of
"onoff_interval" is zero, which disables rcutorture-instigated CPU-hotplug
operations.

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

1 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index af40929e1cb0..d67068d0d2b9 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -61,6 +61,14 @@ nreaders	This is the number of RCU reading threads supported.
                 To properly exercise RCU implementations with preemptible
                 read-side critical sections.
 
+onoff_interval
+                The number of seconds between each attempt to execute a
+                randomly selected CPU-hotplug operation.  Defaults to
+                zero, which disables CPU hotplugging.  In HOTPLUG_CPU=n
+                kernels, rcutorture will silently refuse to do any
+                CPU-hotplug operations regardless of what value is
+                specified for onoff_interval.
+
 shuffle_interval
                 The number of seconds to keep the test threads affinitied
                 to a particular subset of the CPUs, defaults to 3 seconds.