linux-kernel - Re: [PATCH 23/23] sched: Remove sched_set

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Date:   Wed, 22 Apr 2020 09:16:47 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        rostedt@...dmis.org, qais.yousef@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, axboe@...nel.dk,
        daniel.lezcano@...aro.org, sudeep.holla@....com,
        airlied@...hat.com, broonie@...nel.org
Subject: Re: [PATCH 23/23] sched: Remove sched_set_*() return value

On Wed, Apr 22, 2020 at 01:27:42PM +0200, Peter Zijlstra wrote:
> Ingo suggested that since the new sched_set_*() functions are
> implemented using the 'nocheck' variants, they really shouldn't ever
> fail, so remove the return value.
> 
> Cc: axboe@...nel.dk
> Cc: daniel.lezcano@...aro.org
> Cc: sudeep.holla@....com
> Cc: airlied@...hat.com
> Cc: broonie@...nel.org
> Cc: paulmck@...nel.org
> Suggested-by: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  drivers/block/drbd/drbd_receiver.c    |    4 +---
>  drivers/firmware/psci/psci_checker.c  |    3 +--
>  drivers/gpu/drm/msm/msm_drv.c         |    5 +----
>  drivers/platform/chrome/cros_ec_spi.c |    7 +++----
>  include/linux/sched.h                 |    6 +++---
>  kernel/rcu/rcutorture.c               |    5 +----
>  kernel/sched/core.c                   |   12 ++++++------
>  7 files changed, 16 insertions(+), 26 deletions(-)

[ . . . ]

> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -806,10 +806,7 @@ static int rcu_torture_boost(void *arg)
>  	VERBOSE_TOROUT_STRING("rcu_torture_boost started");
>  
>  	/* Set real-time priority. */
> -	if (sched_set_fifo_low(current) < 0) {
> -		VERBOSE_TOROUT_STRING("rcu_torture_boost RT prio failed!");
> -		n_rcu_torture_boost_rterror++;
> -	}
> +	sched_set_fifo_low(current);
>  
>  	init_rcu_head_on_stack(&rbi.rcu);
>  	/* Each pass through the following loop does one boost-test cycle. */

This is the only update of n_rcu_torture_boost_rterror, so it can
be eliminated entirely, for example as shown below.

Other than that, looks good to me!

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index ee27b57..61b0c4f 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -171,7 +171,6 @@ static atomic_t n_rcu_torture_mberror;
 static atomic_t n_rcu_torture_error;
 static long n_rcu_torture_barrier_error;
 static long n_rcu_torture_boost_ktrerror;
-static long n_rcu_torture_boost_rterror;
 static long n_rcu_torture_boost_failure;
 static long n_rcu_torture_boosts;
 static atomic_long_t n_rcu_torture_timers;
@@ -893,10 +892,7 @@ static int rcu_torture_boost(void *arg)
 	VERBOSE_TOROUT_STRING("rcu_torture_boost started");
 
 	/* Set real-time priority. */
-	if (sched_set_fifo_low(current) < 0) {
-		VERBOSE_TOROUT_STRING("rcu_torture_boost RT prio failed!");
-		n_rcu_torture_boost_rterror++;
-	}
+	sched_set_fifo_low(current);
 
 	init_rcu_head_on_stack(&rbi.rcu);
 	/* Each pass through the following loop does one boost-test cycle. */
@@ -1527,11 +1523,10 @@ rcu_torture_stats_print(void)
 		atomic_read(&n_rcu_torture_alloc),
 		atomic_read(&n_rcu_torture_alloc_fail),
 		atomic_read(&n_rcu_torture_free));
-	pr_cont("rtmbe: %d rtbe: %ld rtbke: %ld rtbre: %ld ",
+	pr_cont("rtmbe: %d rtbe: %ld rtbke: %ld ",
 		atomic_read(&n_rcu_torture_mberror),
 		n_rcu_torture_barrier_error,
-		n_rcu_torture_boost_ktrerror,
-		n_rcu_torture_boost_rterror);
+		n_rcu_torture_boost_ktrerror);
 	pr_cont("rtbf: %ld rtb: %ld nt: %ld ",
 		n_rcu_torture_boost_failure,
 		n_rcu_torture_boosts,
@@ -1545,14 +1540,12 @@ rcu_torture_stats_print(void)
 	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
 	if (atomic_read(&n_rcu_torture_mberror) ||
 	    n_rcu_torture_barrier_error || n_rcu_torture_boost_ktrerror ||
-	    n_rcu_torture_boost_rterror || n_rcu_torture_boost_failure ||
-	    i > 1) {
+	    n_rcu_torture_boost_failure || i > 1) {
 		pr_cont("%s", "!!! ");
 		atomic_inc(&n_rcu_torture_error);
 		WARN_ON_ONCE(atomic_read(&n_rcu_torture_mberror));
 		WARN_ON_ONCE(n_rcu_torture_barrier_error);  // rcu_barrier()
 		WARN_ON_ONCE(n_rcu_torture_boost_ktrerror); // no boost kthread
-		WARN_ON_ONCE(n_rcu_torture_boost_rterror); // can't set RT prio
 		WARN_ON_ONCE(n_rcu_torture_boost_failure); // RCU boost failed
 		WARN_ON_ONCE(i > 1); // Too-short grace period
 	}
@@ -2569,7 +2562,6 @@ rcu_torture_init(void)
 	atomic_set(&n_rcu_torture_error, 0);
 	n_rcu_torture_barrier_error = 0;
 	n_rcu_torture_boost_ktrerror = 0;
-	n_rcu_torture_boost_rterror = 0;
 	n_rcu_torture_boost_failure = 0;
 	n_rcu_torture_boosts = 0;
 	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)