[Intel-gfx] [PATCH 1/2] [v3] drm/i915: reference count for i915_hw_contexts

[Daniel Vetter]

On Wed, Apr 03, 2013 at 12:56:11PM +0100, Chris Wilson wrote:
> On Tue, Apr 02, 2013 at 06:27:00PM -0700, Ben Widawsky wrote:
> > On Tue, Apr 02, 2013 at 03:45:42PM -0700, Ben Widawsky wrote:
> > > From: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > > 
> > > In preparation to do analysis of which context was
> > > guilty of gpu hung, store kreffed context pointer
> > > into request struct.
> > > 
> > > This allows us to inspect contexts when gpu is reset
> > > even if those contexts would already be released
> > > by userspace.
> > > 
> > > v2: track i915_hw_context pointers instead of using ctx_ids
> > >     (from Chris Wilson)
> > > 
> > > v3 (Ben): Get rid of do_release() and handle refcounting more compactly.
> > > (recommended by Chris)
> > > 
> > > Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> > > Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> > 
> > Now I remember why my version of reference counting was so much more
> > complicated. In my case, I want to keep the last context around instead
> > of the last context object. To do this we can't do a kref_put until
> > we've switched to the next context (similar to how we manage the context
> > object). I want to do this since the context stores the PPGTT which will
> > currently be in use. I need to switch PDEs at context switch time.
> 
> This seems feasible using requests and a callback from retire. The
> alternative is something hairy like intel_overlay, hence my desire for
> keeping all ring operations as a i915_gem_request.

As long as the request object keeps a ref while the request is still
oustanding and the ring itself keeps a ref to whatever is the currently
last scheduled context, everything should work out fine. So I don't think
we need to jump through any complicated hoops here.

One quick bikeshed on the patch itself though: I'd like to see some static
inlines for kref_get/put on contexts ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch