[Intel-gfx] [PATCH] drm/i915/selftests: Wait for the dma-fence timeout

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-01-17 12:27:50)
> 
> On 17/01/2018 12:15, Chris Wilson wrote:
> > When testing that the timeout fired, we need to be sure we have waited
> > just long enough for the timeout to have occurred and for the softirq
> > (on another cpu) to have completed. Sleeping for an arbitrary amount is
> > prone to error, so wait for the timeout instead and complain if it was
> > too late.
> > 
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=104670
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> >   drivers/gpu/drm/i915/selftests/i915_sw_fence.c | 30 +++++++++-----------------
> >   1 file changed, 10 insertions(+), 20 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/selftests/i915_sw_fence.c b/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
> > index 4fb51deb81a1..f171db16a1c4 100644
> > --- a/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
> > +++ b/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
> > @@ -661,7 +661,7 @@ static int test_dma_fence(void *arg)
> >   {
> >       struct i915_sw_fence *timeout = NULL, *not = NULL;
> >       unsigned long delay = i915_selftest.timeout_jiffies;
> > -     unsigned long end, sleep;
> > +     unsigned long start, end;
> >       struct dma_fence *dma;
> >       int err;
> >   
> > @@ -688,36 +688,26 @@ static int test_dma_fence(void *arg)
> >       }
> >   
> >       /* We round the timeout for the fence up to the next second */
> > -     end = round_jiffies_up(jiffies + delay);
> > +     start = jiffies;
> > +     end = round_jiffies_up(start + delay);
> >   
> > -     sleep = jiffies_to_usecs(delay) / 3;
> > -     usleep_range(sleep, 2 * sleep);
> > -     if (time_after(jiffies, end)) {
> > -             pr_debug("Slept too long, delay=%lu, skipping!\n", delay);
> > -             goto skip;
> > +     if (wait_event_interruptible(timeout->wait,
> > +                                  i915_sw_fence_done(timeout))) {
> > +             err = -EINTR;
> > +             goto err;
> 
> But can now hang forever if broken.

Which is why I allowed it to be interrupted. Maybe wait_event_killable()?

> How about short sleeps in a loop until a timeout?

I kind of like the idea of using the waitqueue now :)

How about if I attach a timer to kick the waitqueue instead.
-Chris