rcu: make rcutorture more vicious: add stutter feature

This patch takes a step towards making rcutorture more brutal by allowing
the test to be automatically periodically paused, with the default being
to run the test for five seconds then pause for five seconds and repeat.
This behavior can be controlled using a new "stutter" module parameter, so
that "stutter=0" gives the old default behavior of running continuously.

Starting and stopping rcutorture more heavily stresses RCU's interaction
with the scheduler, as well as exercising more paths through the
grace-period detection code.

Note that the default to "shuffle_interval" has also been adjusted from
5 seconds to 3 seconds to provide varying overlap with the "stutter"
interval.

I am still unable to provoke the failures that Alexey has been seeing,
even with this patch, but will be doing a few additional things to beef
up rcutorture.

Suggested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 1 deletions

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index 2967a65269d8..02b3d14c0209 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -46,9 +46,15 @@ stat_interval	The number of seconds between output of torture
 
 shuffle_interval
                 The number of seconds to keep the test threads affinitied
-                to a particular subset of the CPUs, defaults to 5 seconds.
+                to a particular subset of the CPUs, defaults to 3 seconds.
                 Used in conjunction with test_no_idle_hz.
 
+stutter         The length of time to run the test before pausing for this
+                same period of time.  Defaults to "stutter=5", so as
+                to run and pause for (roughly) five-second intervals.
+                Specifying "stutter=0" causes the test to run continuously
+                without pausing, which is the old default behavior.
+
 test_no_idle_hz Whether or not to test the ability of RCU to operate in
                 a kernel that disables the scheduling-clock interrupt to
                 idle CPUs.  Boolean parameter, "1" to test, "0" otherwise.