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

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Date:	Mon, 1 Jul 2013 13:55:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
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 Mon, Jul 01, 2013 at 01:20:20PM +0200, Frederic Weisbecker wrote:
> 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?

Ah indeed. I just tripped over the fact that its weird to not test
irqs_disabled() even though we don't have the preempt count.


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