rcutorture: Add callback-flood test

Although RCU is designed to handle arbitrary floods of callbacks, this
capability is not routinely tested.   This commit therefore adds a
cbflood capability in which kthreads repeatedly registers large numbers
of callbacks.  One such kthread is created for each four CPUs (rounding
up), and the test may be controlled by several cbflood_* kernel boot
parameters, which control the number of bursts per flood, the number
of callbacks per burst, the time between bursts, and the time between
floods.  The default values are large enough to exercise RCU's emergency
responses to callback flooding.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Miller <davem@davemloft.net>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 5ae8608ca9f5..0a104be4ad86 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2881,6 +2881,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         Lazy RCU callbacks are those which RCU can
                         prove do nothing more than free memory.
 
+        rcutorture.cbflood_inter_holdoff= [KNL]
+                        Set holdoff time (jiffies) between successive
+                        callback-flood tests.
+
+        rcutorture.cbflood_intra_holdoff= [KNL]
+                        Set holdoff time (jiffies) between successive
+                        bursts of callbacks within a given callback-flood
+                        test.
+
+        rcutorture.cbflood_n_burst= [KNL]
+                        Set the number of bursts making up a given
+                        callback-flood test.  Set this to zero to
+                        disable callback-flood testing.
+
+        rcutorture.cbflood_n_per_burst= [KNL]
+                        Set the number of callbacks to be registered
+                        in a given burst of a callback-flood test.
+
         rcutorture.fqs_duration= [KNL]
                         Set duration of force_quiescent_state bursts.