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

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Message-ID: <bece0d90535709ef39006adb5f481993d6063929.camel@perches.com>
Date:   Tue, 10 Apr 2018 08:14:54 -0700
From:   Joe Perches <joe@...ches.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     yuankuiz@...eaurora.org, Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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>,
        apw@...onical.com
Subject: Re: Subject: [PATCH] [PATCH] time: tick-sched: use bool for
 tick_stopped

On Tue, 2018-04-10 at 14:33 +0200, Peter Zijlstra wrote:
> On Tue, Apr 10, 2018 at 10:00:01AM +0200, Rafael J. Wysocki wrote:
> > On Tue, Apr 10, 2018 at 9:33 AM,  <yuankuiz@...eaurora.org> wrote:
> > > +++ 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.
> 
> Joe, apw, could we get Checkpatch to whinge about _Bool in composite
> types? That should immediately also disqualify using it as the base type
> of bitfields.

Whinging about bool <foo> : <x> seems entirely sensible
and straightforward to do.

I'm not so sure about bool in structs as a patch context
could be adding a bool to local stack definitions and
there's no real ability to determine if the bool is in a
struct or on the stack.

Also, I think there's nothing really wrong with using
bool in structs.  Steven Rostedt's rationale in
https://lkml.org/lkml/2017/11/21/207 isn't really right
as sizeof(int) is 4 not 1 and sizeof(bool) is 1 on arches
without alignment issues.  I believe when using gcc,
sizeof(bool) is always 1 and there may be alignment padding
added on some arches.  Dunno.

But I think the battle is already lost anyway.

git grep -P  '(?<!static|extern)\s+bool\s+\w+\s*;' include | wc -l
1543