Re: [PATCH] time: tick-sched: use bool for tick_stopped

[yuankuiz]

Hi Thomas,

On 2018-04-10 05:10 PM, Thomas Gleixner wrote:
> On Tue, 10 Apr 2018, yuankuiz@xxxxxxxxxxxxxx wrote:
> > On 2018-04-10 04:00 PM, Rafael J. Wysocki wrote:
> > > On Tue, Apr 10, 2018 at 9:33 AM,  <yuankuiz@xxxxxxxxxxxxxx> wrote:
> > > > From: John Zhao <yuankuiz@xxxxxxxxxxxxxx>
> > > >
> > > > Variable tick_stopped returned by tick_nohz_tick_stopped
> > > > can have only true / false 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 unsigned int.
> > > > Moreover, the executed instructions cost could be minimal
> > > > without potiential data type conversion.
> > > >
> > > > Signed-off-by: John Zhao <yuankuiz@xxxxxxxxxxxxxx>
> > > > ---
> > > >  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
[ZJ] 1 bit vs 1 bit. no more.

> for no benefit at all.
[ZJ] tick_stopped is returned by the tick_nohz_tick_stopped() which is 
bool.
The benefit is no any potiential type conversion could be minded.

> Thanks,
>
> 	tglx