[Mesa-dev] [PATCH 2/2] egl, dri: Propagate context priority hint to driver->CreateContext

[Chris Wilson]

On Thu, Apr 06, 2017 at 08:29:55PM -0400, Rob Clark wrote:
> On Thu, Apr 6, 2017 at 3:12 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > Jump through the layers of abstraction between egl and dri in order to
> > feed the context priority attribute through to the backend. This
> > requires us to read the value from the base _egl_context, convert it to
> > a DRI attribute, parse it again in the generic context creater before
> > passing it to the driver as a function parameter.
> >
> > Issues:
> >
> >  * How to pass back the priority of the create context (as it may be
> > modified by the driver) back to EGL?
> 
> Maybe driver provides a bitmask of supportable priority levels, and
> then EGL clamps?  Or a NumPriorityLevels param?  That avoids needing
> to get the value back from the driver and at least works for the
> situations I can think of.  (Ie. either kernel+hw support multiple
> priority levels or it doesn't.)  Maybe with an additional system level
> limit, ie. maybe only compositor can be highest priority.. but that
> seems like a system level thing rather than driver level thing, so
> should be in EGL?

We mirrored our kernel API around nice(2) in that we allow anybody to
reduce their priority, but only a privileged process can raise it above
0. To be accurate, I was going to use the result of the context priority
adjustment to see if the requested level was applied.

I think we can at least do something like

dri2_setup_screen:
	dri2_dpy->*->getCapabilities()

and use disp->Extensions.IMG_context_priority = (LO | MED | HI);
to pass the support up the chain.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre