[Intel-gfx] [PATCH igt] igt/gem_fence_thrash, gem_mmap_gtt: Don't let the device sleep

[Chris Wilson]

Quoting Daniel Vetter (2017-08-23 16:09:50)
> On Wed, Aug 23, 2017 at 03:13:55PM +0100, Chris Wilson wrote:
> > These tests are not intended to exercise runtime pm, but the device
> > going to sleep in the middle of these tests can significantly slow them
> > down as the GTT mmapping is torn down and must be rebuilt. This can be a
> > major nuisance if the device autosuspends many times a second.
> > 
> > These tests differ from typical applications as they are not doing any
> > rendering or utilizing the display which would ordinarily keep the
> > device awake.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> 
> Can we just disable rpm while the test is on? Or at least set the
> autosuspend timer to something huge like 60s, plus exit handler ofc.
> 
> Not as neat uabi as a fd-based wakeref, but has the upside that it doesn't
> require a new kernel. Since we just discussed igt compat in another thread
> ...

We don't depend upon for correct test functionality, just to avoid
emulating the page-fault-of-doom. It's just a nice-to-have from that
pov. The fallback would be to take i915_forcewake_user instead. That's a
bit of an overkill, but both have the drawback of disabling some
important sanity checking by the runtime-pm infra. If we do accept that
some bludging is necessary to help bxt, we should at least add a couple
of tests before the wakeref to see if we can exercise those internal
checks.
 
> Maybe should even extract that into lib/ from pm_rpm.

I carefully stopped before the third instance.
-Chris