[PATCH] drm/i915/selftests: Use preemption timeout on cleanup

[Andi Shyti]

Hi Janusz,

> > > > > +
> > > > >  		cond_resched();
> > > > >  
> > > > > -		if (intel_gt_wait_for_idle(gt, HZ * 3) == -ETIME) {
> > > > > +		if (intel_gt_wait_for_idle(gt, HZ * timeout_ms / 500) == -
> > > ETIME) {
> > > > 
> > > > where is this 500 coming from?
> > > 
> > > / 1000 would convert it to seconds as needed, and / 500 used instead was 
> > > supposed to to mean that we are willing to wait for preempt_timeout_ms * 
> 2.  
> > > Sorry for that shortcut.  Would you like me to provide a clarifying 
> comment, 
> > > or maybe better use explicit 2 * preempt_timeout / 1000 ?
> > 
> > It was clear that you were doubling it, but what's more
> > interesting to know (perhaps in a comment) is why you are
> > choosing to use the double of the timeout_ms instead of other
> > values.
> > 
> > Makes sense?
> 
> Yes, good question.
> 
> Is it possible for more than one bb to hang?  If yes then should we wait 
> longer than the longest preemption timeout?  Before I assumed that maybe we 
> should, just in case, but now, having that revisited and reconsidered, I tend 
> to agree that the longest preempt timeout, perhaps with a small margin (let's 
> say +100ms) should be enough to recover from a single failing test case.  Let 
> me verify if that works for the linked case.

As we agreed offline, I'm going to add this comment you suggested
to your change as a justification to the "/ 500":

/* 2x longest preempt timeout, experimentally determined */

With this:

Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com>

Thanks,
Andi