linux-kernel - Re: [PATCH 04/23] sched,acpi_pad: Convert to sched_set

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Message-ID: <c620bb30-eeee-336b-f8d6-a98e903a48e2@arm.com>
Date:   Wed, 22 Apr 2020 18:45:36 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, rostedt@...dmis.org, qais.yousef@....com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        bsegall@...gle.com, mgorman@...e.de, rafael.j.wysocki@...el.com
Subject: Re: [PATCH 04/23] sched,acpi_pad: Convert to sched_set_fifo*()

On 22/04/2020 13:27, Peter Zijlstra 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.
> 
> In this case, use fifo_low, because it only cares about being above
> SCHED_NORMAL. Effectively no change in behaviour.
> 
> XXX: this driver is still complete crap; why isn't it using proper
> idle injection or at the very least play_idle() ?
> 
> Cc: rafael.j.wysocki@...el.com
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Ingo Molnar <mingo@...nel.org>
> ---
>  drivers/acpi/acpi_pad.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> --- a/drivers/acpi/acpi_pad.c
> +++ b/drivers/acpi/acpi_pad.c
> @@ -136,12 +136,11 @@ static unsigned int idle_pct = 5; /* per
>  static unsigned int round_robin_time = 1; /* second */
>  static int power_saving_thread(void *data)
>  {
> -	struct sched_param param = {.sched_priority = 1};
>  	int do_sleep;
>  	unsigned int tsk_index = (unsigned long)data;
>  	u64 last_jiffies = 0;
>  
> -	sched_setscheduler(current, SCHED_RR, &param);

I was wondering what happened to the SCHED_RR cases but as I can see now
they are handled here and in the next patch.

> +	sched_set_fifo_low(current);
>  
>  	while (!kthread_should_stop()) {
>  		unsigned long expire_time;
> 
>