locktorture: Make the rt_boost factor a tunable

The rt boosting in locktorture has a factor variable s currently large enough
that boosting only happens once every minute or so. Add a tunable to reduce the
factor so that boosting happens more often, to test paths and arrive at failure
modes earlier. With this change, I can set the factor to like 50 and have the
boosting happens every 10 seconds or so.

Tested with boot parameters:
locktorture.torture_type=mutex_lock
locktorture.onoff_interval=1
locktorture.nwriters_stress=8
locktorture.stutter=0
locktorture.rt_boost=1
locktorture.rt_boost_factor=50
locktorture.nlocks=3

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/locking/locktorture.c

@@ -48,6 +48,7 @@ torture_param(int, stat_interval, 60,
 torture_param(int, stutter, 5, "Number of jiffies to run/halt test, 0=disable");
 torture_param(int, rt_boost, 2,
 		"Do periodic rt-boost. 0=Disable, 1=Only for rt_mutex, 2=For all lock types.");
+torture_param(int, rt_boost_factor, 50, "A factor determining how often rt-boost happens.");
 torture_param(int, verbose, 1,
 	     "Enable verbose debugging printk()s");
 
@@ -131,12 +132,12 @@ static void torture_lock_busted_write_unlock(int tid __maybe_unused)
 
 static void __torture_rt_boost(struct torture_random_state *trsp)
 {
-	const unsigned int factor = 50000; /* yes, quite arbitrary */
+	const unsigned int factor = rt_boost_factor;
 
 	if (!rt_task(current)) {
 		/*
-		 * Boost priority once every ~50k operations. When the
-		 * task tries to take the lock, the rtmutex it will account
+		 * Boost priority once every rt_boost_factor operations. When
+		 * the task tries to take the lock, the rtmutex it will account
 		 * for the new priority, and do any corresponding pi-dance.
 		 */
 		if (trsp && !(torture_random(trsp) %
@@ -146,8 +147,9 @@ static void __torture_rt_boost(struct torture_random_state *trsp)
 			return;
 	} else {
 		/*
-		 * The task will remain boosted for another ~500k operations,
-		 * then restored back to its original prio, and so forth.
+		 * The task will remain boosted for another 10 * rt_boost_factor
+		 * operations, then restored back to its original prio, and so
+		 * forth.
 		 *
 		 * When @trsp is nil, we want to force-reset the task for
 		 * stopping the kthread.