linux-kernel - Re: [RFC PATCH 4/4] sched: Consolidate open coded preemptible() checks

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Message-ID: <20130701112019.GB7246@somewhere.redhat.com>
Date:	Mon, 1 Jul 2013 13:20:20 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, Alex Shi <alex.shi@...el.com>,
	Paul Turner <pjt@...gle.com>, Mike Galbraith <efault@....de>,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [RFC PATCH 4/4] sched: Consolidate open coded preemptible()
 checks

On Wed, Jun 26, 2013 at 03:05:11PM +0200, Peter Zijlstra wrote:
> On Thu, Jun 20, 2013 at 10:45:41PM +0200, Frederic Weisbecker wrote:
> > preempt_schedule() and preempt_schedule_context() open
> > code their preemptability checks.
> > 
> > Use the standard API instead for consolidation.
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
> > Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Alex Shi <alex.shi@...el.com>
> > Cc: Paul Turner <pjt@...gle.com>
> > Cc: Mike Galbraith <efault@....de>
> > Cc: Vincent Guittot <vincent.guittot@...aro.org>
> > ---
> >  kernel/context_tracking.c |    3 +--
> >  kernel/sched/core.c       |    4 +---
> >  2 files changed, 2 insertions(+), 5 deletions(-)
> > 
> > diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> > index 6667700..08db730 100644
> > --- a/kernel/context_tracking.c
> > +++ b/kernel/context_tracking.c
> > @@ -88,10 +88,9 @@ void user_enter(void)
> >   */
> >  void __sched notrace preempt_schedule_context(void)
> >  {
> > -	struct thread_info *ti = current_thread_info();
> >  	enum ctx_state prev_ctx;
> >  
> > -	if (likely(ti->preempt_count || irqs_disabled()))
> > +	if (likely(!preemptible()))
> >  		return;
> >  
> 
> #ifdef CONFIG_PREEMPT_COUNT
> # define preemptible()  (preempt_count() == 0 && !irqs_disabled())
> #else
> # define preemptible()  0
> #endif
> 
> 
> Wouldn't that give a problem for !PREEMPT_COUNT?

preempt_schedule_context() depends on CONFIG_PREEMPT which depends on
CONFIG_PREEMPT_COUNT, so that should work. Or I missed something?
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