linux-kernel - Re: [PATCH] tick/sched: Drop duplicated tick

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Message-ID: <20190522121837.GA11692@lerouge>
Date:   Wed, 22 May 2019 14:18:41 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] tick/sched: Drop duplicated tick_sched.inidle

On Wed, May 22, 2019 at 11:29:06AM +0800, Peter Xu wrote:
> It is set before entering idle and cleared when quitting idle, though
> it seems to be a complete duplicate of tick_sched.idle_active.  We
> should probably be able to use any one of them to replace the other.

Not exactly.

@inidle is set on idle entry and cleared on idle exit.
@idle_active is the same but it's cleared during idle interrupts
so that idle_sleeptime only account real idle time.

And note below:

> @@ -1017,7 +1015,7 @@ void tick_nohz_irq_exit(void)
>  {
>  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
>  
> -	if (ts->inidle)
> +	if (ts->idle_active)
>  		tick_nohz_start_idle(ts);

idle_active will always be cleared here from tick_nohz_irq_enter().
We actually want to conditionally set it again depending on the inidle value.

Thanks.