linux-kernel - Re: Subject: [PATCH] [PATCH] time: tick-sched: use bool for tick

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Message-ID: <alpine.DEB.2.21.1804101110080.2058@nanos.tec.linutronix.de>
Date:   Tue, 10 Apr 2018 11:10:53 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     yuankuiz@...eaurora.org
cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        aulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...nel.org>,
        Len Brown <len.brown@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pm-owner@...r.kernel.org
Subject: Re: Subject: [PATCH] [PATCH] time: tick-sched: use bool for
 tick_stopped

On Tue, 10 Apr 2018, yuankuiz@...eaurora.org wrote:
> On 2018-04-10 04:00 PM, Rafael J. Wysocki wrote:
> > On Tue, Apr 10, 2018 at 9:33 AM,  <yuankuiz@...eaurora.org> wrote:
> > > From: John Zhao <yuankuiz@...eaurora.org>
> > > 
> > > Variable tick_stopped returned by tick_nohz_tick_stopped
> > > can have only true / forse values. Since the return type
> > > of the tick_nohz_tick_stopped is also bool, variable
> > > tick_stopped nice to have data type as bool in place of int.
> > > Moreover, the executed instructions cost could be minimal
> > > without potiential data type conversion.
> > > 
> > > Signed-off-by: John Zhao <yuankuiz@...eaurora.org>
> > > ---
> > >  kernel/time/tick-sched.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
> > > index 6de959a..4d34309 100644
> > > --- a/kernel/time/tick-sched.h
> > > +++ b/kernel/time/tick-sched.h
> > > @@ -48,8 +48,8 @@ struct tick_sched {
> > >         unsigned long                   check_clocks;
> > >         enum tick_nohz_mode             nohz_mode;
> > > 
> > > +       bool                            tick_stopped    : 1;
> > >         unsigned int                    inidle          : 1;
> > > -       unsigned int                    tick_stopped    : 1;
> > >         unsigned int                    idle_active     : 1;
> > >         unsigned int                    do_timer_last   : 1;
> > >         unsigned int                    got_idle_tick   : 1;
> > 
> > I don't think this is a good idea at all.
> > 
> > Please see https://lkml.org/lkml/2017/11/21/384 for example.
> [ZJ] Thanks for this sharing. Looks like, this patch fall into the case of
> "Maybe".

This patch falls into the case 'pointless' because it adds extra storage
for no benefit at all.

Thanks,

	tglx