[Intel-gfx] [PATCH 6/8] drm/i915: reprogram NOA muxes on context switch when using perf

[Chris Wilson]

Quoting Lionel Landwerlin (2018-04-25 12:45:19)
> If some of the contexts submitting workloads to the GPU have been
> configured to shutdown slices/subslices, we might loose the NOA
> configurations written in the NOA muxes. We need to reprogram them at
> context switch.

On every single batchbuffer, no way. That's around a 33% latency hit,
ignoring the cost of what's inside the wa_bb.

If they are not context saved, userspace isn't going to be allowed to
modify them. So why do we need this? If they not context saved, then the
kernel needs to control them and doesn't need to reset around every
batch, just the one's that want non-default (fancier if we handle
preemption)?
-Chris