linux-kernel - Re: [PATCH 2/2] sched: Move the sleeping while atomic checks early in cond

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Date:	Fri, 10 Jul 2009 17:12:08 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched: Move the sleeping while atomic checks early
 in cond_resched()

On Fri, 2009-07-10 at 17:08 +0200, Frederic Weisbecker wrote:
> On Fri, Jul 10, 2009 at 04:59:55PM +0200, Peter Zijlstra wrote:
> > On Fri, 2009-07-10 at 16:49 +0200, Frederic Weisbecker wrote:
> > 
> > > index 0cb0d8d..e357dc7 100644
> > > --- a/include/linux/sched.h
> > > +++ b/include/linux/sched.h
> > > @@ -2279,11 +2279,13 @@ extern int _cond_resched(void);
> > >  #ifdef CONFIG_PREEMPT_BKL
> > >  static inline int cond_resched(void)
> > >  {
> > > +	might_sleep();
> > >  	return 0;
> > >  }
> > >  #else
> > >  static inline int cond_resched(void)
> > >  {
> > > +	might_sleep();
> > >  	return _cond_resched();
> > >  }
> > >  #endif
> > 
> > # define might_resched() _cond_resched()
> 
> 
> Argh, indeed.
> I thought might_sleep() only wrapped __might_sleep(__FILE__, __LINE__)
> 
>  
> > # define might_sleep() \
> > 	do { __might_sleep(__FILE__, __LINE__); might_resched(); } while (0)
> > 
> > 
> > Doesn't seem to make it any better that, but yeah, moving that
> > __might_sleep() did occur to me earlier today when I touched that code.
> 
> 
> Ok.
> 
> Another idea: if cond_resched() was a macro and __might_sleep() was
> called inside, the given __FILE__ __LINE__ would be much more useful.
> 
> Only the backtraces would be useful in the current state, __FILE__
> and __LINE__ point to sched.h, which is not exactly what is needed,
> right?

Right. There's some CONFIG_PREEMPT_BKL clutter in sched.h but I think we
could largely fold might_sleep() and cond_resched().

Ingo?

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