linux-kernel - Re: [PATCH 16/23] sched,watchdog: Convert to sched_set

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Message-ID: <20200422085155.7549ca94@gandalf.local.home>
Date:   Wed, 22 Apr 2020 08:51:55 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        qais.yousef@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, wim@...ux-watchdog.org,
        Christophe Leroy <christophe.leroy@....fr>
Subject: Re: [PATCH 16/23] sched,watchdog: Convert to sched_set_fifo()

On Wed, 22 Apr 2020 13:27:35 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> Because SCHED_FIFO is a broken scheduler model (see previous patches)
> take away the priority field, the kernel can't possibly make an
> informed decision.
> 
> Effectively changes prio from 99 to 50.

Hmm, this being a watchdog, and looking at commit 38a1222ae4f364d
("watchdog: core: make sure the watchdog worker always works")

I wonder if we should add a sched_set_high(), or have some other kind of
watchdog handler that is guaranteed to trigger.

-- Steve


> 
> Cc: wim@...ux-watchdog.org
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Ingo Molnar <mingo@...nel.org>
> ---
>  drivers/watchdog/watchdog_dev.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -1144,14 +1144,13 @@ void watchdog_dev_unregister(struct watc
>  int __init watchdog_dev_init(void)
>  {
>  	int err;
> -	struct sched_param param = {.sched_priority = MAX_RT_PRIO - 1,};
>  
>  	watchdog_kworker = kthread_create_worker(0, "watchdogd");
>  	if (IS_ERR(watchdog_kworker)) {
>  		pr_err("Failed to create watchdog kworker\n");
>  		return PTR_ERR(watchdog_kworker);
>  	}
> -	sched_setscheduler(watchdog_kworker->task, SCHED_FIFO, &param);
> +	sched_set_fifo(watchdog_kworker->task);
>  
>  	err = class_register(&watchdog_class);
>  	if (err < 0) {
>