[Intel-gfx] [PATCH igt] igt/perf_pmu: Recalibrate interrupt loop.

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-11-24 09:11:06)
> 
> On 23/11/2017 15:03, Chris Wilson wrote:
> > We have to be careful in our calibration loop, too slow and we timeout,
> > too fast and we don't emit an interrupt! On fast legacy devices, we
> > would overflow the calibration calcuation...
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> > -     sz = ALIGN(sz, sizeof(uint32_t));
> > +     sz = calibrate_nop(gem_fd, 1e6 / target);
> > +     gem_quiescent_gpu(gem_fd);
> > +
> > +     fd = open_pmu(I915_PMU_INTERRUPTS);
> > +     spin = igt_spin_batch_new(gem_fd, 0, 0, 0);
> 
> What's the spin batch for?

It's just a plug to ensure that the queue of calibrated execs don't start
executing before we're waiting on them. Instead of doing exec + sync, we
want to switch to exec[N] + sync.
-Chris