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From:   "Joel Fernandes (Google)" <joel@joelfernandes.org>
To:     linux-kernel@vger.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ingo Molnar <mingo@redhat.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Mel Gorman <mgorman@suse.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Valentin Schneider <vschneid@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        kernel-team@android.com, John Stultz <jstultz@google.com>,
        Joel Fernandes <joelaf@google.com>,
        Qais Yousef <qais.yousef@arm.com>,
        Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        "Connor O'Brien" <connoro@google.com>
Subject: [PATCH RFC 3/3] locktorture: Make the rt_boost factor a tunable
Date:   Wed, 23 Nov 2022 01:21:04 +0000
Message-Id: <20221123012104.3317665-4-joel@joelfernandes.org>
In-Reply-To: <20221123012104.3317665-1-joel@joelfernandes.org>
References: <20221123012104.3317665-1-joel@joelfernandes.org>
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The rt boosting in locktorture has a factor variable large enough that
boosting only happens once every minute or so. Add a tunable to educe
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>
---
 kernel/locking/locktorture.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 5a388ac96a9b..e4529c2166e9 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -47,6 +47,7 @@ torture_param(int, stat_interval, 60,
 	     "Number of seconds between stats printk()s");
 torture_param(int, stutter, 5, "Number of jiffies to run/halt test, 0=disable");
 torture_param(int, rt_boost, 0, "Perform an rt-boost from the writer, always 1 for rtmutex_lock");
+torture_param(int, rt_boost_factor, 50000, "A factor determining how often rt-boost happens");
 torture_param(int, verbose, 1,
 	     "Enable verbose debugging printk()s");
 torture_param(int, nlocks, 1,
@@ -132,15 +133,15 @@ 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; /* yes, quite arbitrary */
 
 	if (!rt_boost)
 		return;
 
 	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) %
@@ -150,8 +151,9 @@ 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.
-- 
2.38.1.584.g0f3c55d4c2-goog