linux-kernel - Re: [PATCH RFC 3/3] locktorture: Make the rt

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Date:   Wed, 21 Dec 2022 12:28:39 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
CC:     <linux-kernel@...r.kernel.org>, Ben Segall <bsegall@...gle.com>,
        "Daniel Bristot de Oliveira" <bristot@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Valentin Schneider <vschneid@...hat.com>,
        "Vincent Guittot" <vincent.guittot@...aro.org>,
        <kernel-team@...roid.com>, John Stultz <jstultz@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Qais Yousef <qais.yousef@....com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Connor O'Brien <connoro@...gle.com>
Subject: Re: [PATCH RFC 3/3] locktorture: Make the rt_boost factor a tunable

On 2022-11-23 at 01:21:04 +0000, Joel Fernandes (Google) wrote:
> 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@...lfernandes.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
Maybe I understand incorrectly, the code is
cxt.nrealwriters_stress * factor * 2, should it be 2 rather than 10?
May I know where the 10 comes from?

thanks,
Chenyu