rcutorture: Permit holding off CPU-hotplug operations during boot

When rcutorture is started automatically at boot time, it might well
also start CPU-hotplug operations at that time, which might not be
desirable.  This commit therefore adds an rcutorture parameter that
allows CPU-hotplug operations to be held off for the specified number
of seconds after the start of boot.

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

1 files changed, 11 insertions, 2 deletions

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index d67068d0d2b9..01a809b1dbc6 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -69,6 +69,13 @@ onoff_interval
                 CPU-hotplug operations regardless of what value is
                 specified for onoff_interval.
 
+onoff_holdoff   The number of seconds to wait until starting CPU-hotplug
+                operations.  This would normally only be used when
+                rcutorture was built into the kernel and started
+                automatically at boot time, in which case it is useful
+                in order to avoid confusing boot-time code with CPUs
+                coming and going.
+
 shuffle_interval
                 The number of seconds to keep the test threads affinitied
                 to a particular subset of the CPUs, defaults to 3 seconds.
@@ -277,5 +284,7 @@ The following script may be used to torture RCU:
 
 The output can be manually inspected for the error flag of "!!!".
 One could of course create a more elaborate script that automatically
-checked for such errors.  The "rmmod" command forces a "SUCCESS" or
-"FAILURE" indication to be printk()ed.
+checked for such errors.  The "rmmod" command forces a "SUCCESS",
+"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed.  The first
+two are self-explanatory, while the last indicates that while there
+were no RCU failures, CPU-hotplug problems were detected.