linux-kernel - Re: [PATCH tip/core/rcu 4/9] sched: add is_idle_task() to handle invalidated uses of idle

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Date:	Wed, 16 Nov 2011 11:54:36 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	patches@...aro.org, "Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 4/9] sched: add is_idle_task() to handle
 invalidated uses of idle_cpu()

On Tue, Nov 15, 2011 at 01:13:02PM -0800, Josh Triplett wrote:
> On Tue, Nov 15, 2011 at 12:28:00PM -0800, Paul E. McKenney wrote:
> > From: Paul E. McKenney <paul.mckenney@...aro.org>
> > 
> > Commit 908a3283 (Fix idle_cpu()) invalidated some uses of idle_cpu(),
> > which used to say whether or not the CPU was running the idle task,
> > but now instead says whether or not the CPU is running the idle task
> > in the absence of pending wakeups.  Although this new implementation
> > gives a better answer to the question "is this CPU idle?", it also
> > invalidates other uses that were made of idle_cpu().
> > 
> > This commit therefore introduces a new is_idle_task() API member
> > that determines whether or not the specified task is one of the
> > idle tasks, allowing open-coded "->pid == 0" sequences to be replaced
> > by something more meaningful.
> > 
> > Suggested-by: Josh Triplett <josh@...htriplett.org>
> > Suggested-by: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  include/linux/sched.h |    1 +
> >  kernel/sched.c        |    9 +++++++++
> >  2 files changed, 10 insertions(+), 0 deletions(-)
> > 
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 68daf4f..4b1077b 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -2071,6 +2071,7 @@ extern int sched_setscheduler(struct task_struct *, int,
> >  extern int sched_setscheduler_nocheck(struct task_struct *, int,
> >  				      const struct sched_param *);
> >  extern struct task_struct *idle_task(int cpu);
> > +extern int is_idle_task(struct task_struct *p);
> 
> The kernel has a bool type; please use it here rather than int, to make
> the return value more obvious.
> 
> Also, any particular reason not to make this a static inline?

That does work for all the uses thus far, so made both suggested changes.

							Thanx, Paul

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