Re: [igt-dev] [PATCH i-g-t] igt/kms_flip: Allow reported vblank times to be in the future

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Ville Syrjälä (2018-05-11 14:37:31)
> On Thu, May 10, 2018 at 05:04:34PM +0100, Chris Wilson wrote:
> > The vblank timestamp is given for the end of the vblank, but the
> > hardware may report the vblank before that point (so the kernel computes
> > a timestamp in the future), and userspace may then see the vblank event
> > that says the actual start-of-scanout has yet to happen. All this is
> > perfectly legal and can be observed in practice.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106087
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >  tests/kms_flip.c | 7 -------
> >  1 file changed, 7 deletions(-)
> > 
> > diff --git a/tests/kms_flip.c b/tests/kms_flip.c
> > index 3d6fe948d..5b0d07cc2 100644
> > --- a/tests/kms_flip.c
> > +++ b/tests/kms_flip.c
> > @@ -480,13 +480,6 @@ static void check_state(const struct test_output *o, const struct event_state *e
> >       if (es->count == 0)
> >               return;
> >  
> > -     timersub(&es->current_ts, &es->last_received_ts, &diff);
> > -     igt_assert_f(timercmp(&es->last_received_ts, &es->current_ts, <),
> 
> last_received_ts is the time we received the previous event isn't it?

Hmm, I thought it was the timestamp of the last received, which would
be the most recent event...

> So somehow our current event's kernel reported timestamp is older than the
> the time we received the previous event. So the kernel failed to send
> events when it was supposed to, or we failed to process them in a timely
> fashion perhaps?

(kms_flip:1495) DEBUG: name = vblank
last_ts = 326.737520
last_received_ts = 326.737347
last_seq = 15665
current_ts = 326.904242
current_received_ts = 328.153186
current_seq = 15675
count = 66
seq_step = 10
(kms_flip:1495) DEBUG: name = vblank
last_ts = 326.904242
last_received_ts = 328.153186
last_seq = 15675
current_ts = 328.137985
current_received_ts = 328.153386
current_seq = 15749
count = 67
seq_step = 10

Ok, should we have rejected the earlier vblank for having a received_ts
more than a frame into the future?
-Chris
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