[Intel-gfx] [PATCH] drm/i915/selftest: If reconfigure_sseu is busy, try again

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-11-26 17:00:53)
> 
> On 26/11/2019 16:47, Chris Wilson wrote:
> > Following 58b4c1a07ada ("drm/i915: Reduce nested prepare_remote_context()
> > to a trylock"), we punt to the caller if the local intel_context
> > happens to be busy as we try to rewrite the sseu (due to retiring in
> > another thread). As the interlude should be short, spin until the lock
> > is available.
> > 
> > The regret for using mutex_trylock() and not an atomic insertion of the
> > barrier is growing...
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> >   drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
> > index 2ea4790f3721..571cc996577c 100644
> > --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
> > +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
> > @@ -1197,7 +1197,10 @@ __sseu_test(const char *name,
> >       if (ret)
> >               goto out_pm;
> >   
> > -     ret = intel_context_reconfigure_sseu(ce, sseu);
> > +     do {
> > +             ret = intel_context_reconfigure_sseu(ce, sseu);
> > +             cond_resched();
> > +     } while (ret == -EAGAIN);
> >       if (ret)
> >               goto out_spin;
> >   
> > 
> 
> Hm I looked at the selftests, saw error is correctly propagated, and 
> concluded it will be fine. I missed the problem selftests will not 
> actually retry. But wait, can we even count that userspace will if all 
> of a sudden ctx.set_param starts returning -EAGAIN sporadically? Feels 
> like we may need to revert.

We invoke the principle of drmIoctl() catches -EAGAIN.
-Chris