linux-kernel - Re: [PATCH v2 1/3] rcu: Assign higher prio to RCU threads if rcutorture is built-in

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Date:   Wed, 20 Jun 2018 10:10:41 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Byungchul Park <byungchul.park@....com>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        peterz@...radead.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 1/3] rcu: Assign higher prio to RCU threads if
 rcutorture is built-in

On Tue, Jun 19, 2018 at 03:14:17PM -0700, Joel Fernandes wrote:
> From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
> 
> rcutorture boost tests fail even with CONFIG_RCU_BOOST set because
> rcutorture's threads are equal priority to the default RCU kthreads (RT
> class with priority of 1).
> 
> This patch checks if RCU torture is built into the kernel and if so,
> assigns a higher priority to the RCU threads. With this the rcutorture
> boost tests pass.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>

I queued all three for testing and further review.  I reworked the commit
logs a bit and also pulled the error string onto one line to make it
easier on people grepping for the message.  Please let me know if I
messed anything up.

							Thanx, Paul

> ---
>  kernel/rcu/tree.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index deb2508be923..92c29439eba6 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3884,12 +3884,16 @@ static int __init rcu_spawn_gp_kthread(void)
>  	struct task_struct *t;
> 
>  	/* Force priority into range. */
> -	if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
> +	if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
> +	    && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
> +		kthread_prio = 2;
> +	else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
>  		kthread_prio = 1;
>  	else if (kthread_prio < 0)
>  		kthread_prio = 0;
>  	else if (kthread_prio > 99)
>  		kthread_prio = 99;
> +
>  	if (kthread_prio != kthread_prio_in)
>  		pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
>  			 kthread_prio, kthread_prio_in);
> -- 
> 2.18.0.rc1.244.gcf134e6275-goog
>