linux-kernel - Re: [tip:sched/core] sched: Use bool type for rq->idle_at

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Message-ID: <20110511111915.GF18521@elte.hu>
Date:	Wed, 11 May 2011 13:19:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	rakib.mullick@...il.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched: Use bool type for rq->idle_at_tick


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Sat, 2011-04-30 at 07:16 +0000, tip-bot for Rakib Mullick wrote:
> > Commit-ID:  eea502ffd4aeef233b5eadbde405a9df92d57a5e
> > Gitweb:     http://git.kernel.org/tip/eea502ffd4aeef233b5eadbde405a9df92d57a5e
> > Author:     Rakib Mullick <rakib.mullick@...il.com>
> > AuthorDate: Sat, 30 Apr 2011 00:01:02 +0600
> > Committer:  Ingo Molnar <mingo@...e.hu>
> > CommitDate: Sat, 30 Apr 2011 00:17:14 +0200
> > 
> > sched: Use bool type for rq->idle_at_tick
> > 
> > Searching over the scheduler code for uses of rq->idle_at_tick
> > shows us that it's used for making TRUE/FALSE decision.
> > 
> > Still its type is 'unsigned char' so using 'bool' would be
> > cleaner.
> > 
> > Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Link: http://lkml.kernel.org/r/1304100062.19359.6.camel@localhost.localdomain
> > Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > ---
> >  kernel/sched.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index f11a2a5..a492209 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -505,7 +505,7 @@ struct rq {
> >  
> >  	unsigned long cpu_power;
> >  
> > -	unsigned char idle_at_tick;
> > +	bool idle_at_tick;
> >  	/* For active balancing */
> >  	int post_schedule;
> >  	int active_balance;
> 
> Right, so the problem I have with using bool in structures is that
> sizeof(_Bool) is not well defined by the C standard and is
> implementation dependent, meaning the struct rq layout can change
> between gcc versions, architectures or even between optimization levels.
> 
> So for structures where the layout is relevant we must avoid bool.

Okay, zapped it stays then.

Thanks,

	Ingo
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