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

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Date:   Thu, 23 May 2019 13:32:54 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Frederic Weisbecker <frederic@...nel.org>
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 02:18:41PM +0200, Frederic Weisbecker wrote:
> 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.

You are right; I've missed the calls from irq enter/exit. Thanks, Frederic.

-- 
Peter Xu