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

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Message-ID: <20090710161034.GB22049@elte.hu>
Date:	Fri, 10 Jul 2009 18:10:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched: Move the sleeping while atomic checks early
	in cond_resched()


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> 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?

Yep - CONFIG_PREEMPT_BKL wont ever come back so any legacy related 
to it should be removed. (That doesnt mean it wont crash or 
misbehave, this code is quite fragile.)

	Ingo
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