linux-kernel - Re: [PATCH v9 05/10] cpuidle: Return nohz hint from cpuidle

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Date:   Fri, 6 Apr 2018 16:23:56 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Ilsche <thomas.ilsche@...dresden.de>,
        Doug Smythies <dsmythies@...us.net>,
        Rik van Riel <riel@...riel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Mike Galbraith <mgalbraith@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>
Subject: Re: [PATCH v9 05/10] cpuidle: Return nohz hint from cpuidle_select()

On Fri, Apr 06, 2018 at 09:58:37AM +0200, Peter Zijlstra wrote:
> On Fri, Apr 06, 2018 at 04:44:14AM +0200, Frederic Weisbecker wrote:
> > You can move that to tick_sched_do_timer() to avoid code duplication.
> 
> I expect the reason I didn't was that it didn't have @ts, but that's
> easily fixable.
> 
> > Also these constants are very opaque. And even with proper symbols it wouldn't look
> > right to extend ts->inidle that way.
> > 
> > Perhaps you should add a field such as ts->got_idle_tick under the boolean fields
> > after the below patch:
> 
> > @@ -45,14 +45,17 @@ struct tick_sched {
> >  	struct hrtimer			sched_timer;
> >  	unsigned long			check_clocks;
> >  	enum tick_nohz_mode		nohz_mode;
> > +
> > +	unsigned int			inidle		: 1;
> > +	unsigned int			tick_stopped	: 1;
> > +	unsigned int			idle_active	: 1;
> > +	unsigned int			do_timer_last	: 1;
> 
> That would generate worse code, but yes, the C might be prettier.

Well, not too bad I think. MOV become OR/AND, the rest is just
TESTs...