[Intel-gfx] [PATCH igt] lib/dummyload: Pad with a few nops so that we do not completely hog the system

[Chris Wilson]

Quoting Mika Kuoppala (2017-08-16 15:45:54)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > Part of the attraction of using a recursive batch is that it is
> > hard on the system (executing the "function" call is apparently
> > quite expensive). However, the GPU may hog the entire system for
> > a few minutes, preventing even NMI. Quite why this is so is unclear,
> > but presumably it relates to the PM_INTRMSK workaround on gen6/gen7.
> > If we give the system a break by having the GPU execute a few nops
> > between function calls, that appears enough to keep SNB out of
> > trouble.
> >
> 
> Can we trip into the same pit with igt_hang? It has tight
> recurse. Adding few noops makes the hangcheck sampler
> to hit more sparsely and slow the verdict of hang.

And a few others. The reason we stuck the invalid op in there in the
first place was because we didn't have the PM_INTRMSK w/a in place and
we could take out the system. It's that I fear is going wrong, but we
always call gen6_sanitize_rps_pm_mask() now. Ville says that
I915_WRITE(GEN6_RP_CONTROL, 0) is just as fatal. So we may have to
rethink gen6_disable_rps().
-Chris