[Intel-gfx] [PATCH v5 3/4] drm/i915/bdw: Pin the context backing objects to GGTT on-demand

[Daniel Vetter]

On Tue, Nov 18, 2014 at 03:32:46PM +0000, Daniel, Thomas wrote:
> > -----Original Message-----
> > From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel
> > Vetter
> > Sent: Tuesday, November 18, 2014 3:11 PM
> > To: Daniel, Thomas
> > Cc: Daniel Vetter; intel-gfx at lists.freedesktop.org
> > Subject: Re: [Intel-gfx] [PATCH v5 3/4] drm/i915/bdw: Pin the context
> > backing objects to GGTT on-demand
> > 
> > On Tue, Nov 18, 2014 at 02:51:52PM +0000, Daniel, Thomas wrote:
> > > > -----Original Message-----
> > > > From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of
> > > > Daniel Vetter
> > > > Sent: Tuesday, November 18, 2014 2:33 PM
> > > > To: Daniel, Thomas
> > > > Cc: Daniel Vetter; intel-gfx at lists.freedesktop.org
> > > > Subject: Re: [Intel-gfx] [PATCH v5 3/4] drm/i915/bdw: Pin the
> > > > context backing objects to GGTT on-demand
> > > >
> > > > On Tue, Nov 18, 2014 at 10:48:09AM +0000, Daniel, Thomas wrote:
> > > > > > -----Original Message-----
> > > > > > From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org]
> > > > > > On Behalf Of Daniel, Thomas
> > > > > > Sent: Tuesday, November 18, 2014 9:28 AM
> > > > > > To: Daniel Vetter
> > > > > > Cc: intel-gfx at lists.freedesktop.org
> > > > > > Subject: Re: [Intel-gfx] [PATCH v5 3/4] drm/i915/bdw: Pin the
> > > > > > context backing objects to GGTT on-demand
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf
> > > > > > > Of Daniel Vetter
> > > > > > > Sent: Monday, November 17, 2014 6:09 PM
> > > > > > > To: Daniel, Thomas
> > > > > > > Cc: intel-gfx at lists.freedesktop.org
> > > > > > > Subject: Re: [Intel-gfx] [PATCH v5 3/4] drm/i915/bdw: Pin the
> > > > > > > context backing objects to GGTT on-demand
> > > > > > >
> > > > > > > On Thu, Nov 13, 2014 at 10:28:10AM +0000, Thomas Daniel wrote:
> > > > > > > > diff --git a/drivers/gpu/drm/i915/i915_drv.h
> > > > > > > > b/drivers/gpu/drm/i915/i915_drv.h index 059330c..3c7299d
> > > > > > > > 100644
> > > > > > > > --- a/drivers/gpu/drm/i915/i915_drv.h
> > > > > > > > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > > > > > > > @@ -655,6 +655,7 @@ struct intel_context {
> > > > > > > >  	struct {
> > > > > > > >  		struct drm_i915_gem_object *state;
> > > > > > > >  		struct intel_ringbuffer *ringbuf;
> > > > > > > > +		int unpin_count;
> > > > > > >
> > > > > > > Pinning is already refcounted. Why this additional refcount?
> > > > > >
> > > > > > The vma.pin_count is only allocated 4 bits of storage.  If this
> > > > > > restriction can be lifted then I can use that.
> > > >
> > > > Those 4 bits are good enough for legacy contexts, so I wonder a bit
> > > > what's so massively different for execlist contexts.
> > > With execlists, in order to dynamically unpin the LRC backing object
> > > and ring buffer object when not required we take a reference for each
> > > execlist request that uses them (remember that the execlist request
> > > lifecycle is currently different from the execbuffer request).  This
> > > can be a lot, especially in some of the less sane i-g-t tests.
> > 
> > Why?
> > 
> > Presuming the buffer objects is properly pushed onto the active list you only
> > need to pin while doing the command submission up to the point where
> > you've committed the buffer object to the active list.
> This is not currently the case.  Using the active list for context
> object management is one of the refactoring tasks, as we agreed.

Actually I even lied, you need to pin the current context and you can only
throw the old one you've just switched out. Becuase the request for the
next batch/ctx combo will complete after the switched happened this all
works out.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch