[Intel-gfx] [PATCH 1/2] drm/i915/selftests: Calculate maximum ring size for preemption chain

[Chris Wilson]

Quoting Chris Wilson (2019-03-21 18:38:53)
> Quoting Caz Yokoyama (2019-03-21 18:41:10)
> > inline
> > -caz
> > On Thu, 2019-03-21 at 07:37 +0000, Chris Wilson wrote:
> > > 32 is too many for the likes of kbl, and in order to insert that many
> > Not only kbl. ring_size is 25 on my cfl.
> > 
> > > requests into the ring requires us to declare the first few hung --
> > The hung is not caused by 32. It is caused by accumulation of requests
> > for all prime numbers.
> 
> Sure, but the design of the test is that we don't care for more than
> ring_size.

And you can't have more than ring_size requests without hanging on the
spinner. If we pick the maximum that allows for a prime number larger
than ring_size, it hangs irrespective of whether or not you remember to
flush the lo.ctx in between.
-Chris