Re: [PATCH] Return value from schedule()

[Ingo Molnar <mingo@elte.hu>]

* Matthew Wilcox <matthew@wil.cx> wrote:

> In some circumstances, you want to wait for an event to happen.  let's 
> assume that it's a hardware event, so you can't just add a notifier of 
> some kind, you have to poll.  Here's an example:
> 
> On Wed, Sep 03, 2008 at 03:57:13PM -0700, Stephen Hemminger wrote:
> >  			return -ETIMEDOUT;
> > -		udelay(10);
> > +		if (signal_pending(current))
> > +			return -EINTR;
> > +		schedule();
> 
> If there's no other task ready to run, schedule() could return in much
> less than 10 microseconds (actually, it could return in much less than
> 10 microseconds even if another task does run, but let's ignore that case).
> 
> If schedule() returned whether or not it had scheduled another task, we
> could do something like:
> 
> 		if (!schedule())
> 			udelay(10);

hm, i'm not really sure - this really just seems to be a higher prio 
variant of yield() combined with some weird code. Do we really want to 
promote such arguably broken behavior? If there's any chance of any 
polling to take a material amount of CPU time it should be event driven 
to begin with.

	Ingo