[Intel-gfx] [PATCH] drm/i915/execlists: Skip a lite-restore immediately prior to a context-completion

[Chris Wilson]

Quoting Chris Wilson (2017-11-16 22:25:45)
> Quoting Chris Wilson (2017-11-16 22:11:30)
> > If we are about to do another context-switch in the near future skip
> > doing performing a lite-restore now. (Forcing a lite-restore just before
> > a context-switch effectively doubles the cost of that context-switch, so
> > long as we can handle the interrupt and resubmit before the GPU powers
> > down, which under normal conditions is expected.)
> > 
> > Coincidentally, skipping a lite-restore just before idling also prevents
> > (not entirely, but the window for occurrence now depends on the next
> > context completing within the same period and we have already noted that
> > we can resubmit faster than the GPU can context switch to make this
> > worthwhile) an issue on bxt/glk where it may become confused in an attempt
> > to lite-restore an already idle context, after which nothing is quite the
> > same again.
> 
> Well only testing will tell...

The answer is no. (Though BAT hit an entirely new and scary problem.)

We can go back to the discussion of when we might not want to
lite-restore in peace, without the nuisance of trying to w/a hw features.
-Chris