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Date:   Fri, 9 Dec 2022 08:37:59 -0800
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org,
        Josh Triplett <josh@joshtriplett.org>,
        "Paul E. McKenney" <paulmck@kernel.org>, rcu@vger.kernel.org,
        connoro@google.com
Subject: Re: [PATCH v2 2/2] locktorture: Make the rt_boost factor a tunable
Message-ID: <20221209163759.6s7pqf5wdvy32ywn@offworld>
References: <20221209022305.321149-1-joel@joelfernandes.org>
 <20221209022305.321149-2-joel@joelfernandes.org>
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On Fri, 09 Dec 2022, Joel Fernandes (Google) wrote:

>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>

>---
> 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 8968fd65a90d..b64a528e511c 100644
>--- a/kernel/locking/locktorture.c
>+++ b/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");
> torture_param(int, nlocks, 1,
>@@ -133,12 +134,12 @@ 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

Nit: maybe refer to it as 'rt_boost_factor'?

> 		 * for the new priority, and do any corresponding pi-dance.
> 		 */
> 		if (trsp && !(torture_random(trsp) %
>@@ -148,8 +149,9 @@ 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.
>-- 
>2.39.0.rc1.256.g54fd8350bd-goog
>