Re: [Intel-gfx] [PATCH v3] uapi/drm/i915: Document memory residency and Flat-CCS capability of obj

[Ramalingam C <ramalingam.c@intel.com>]

On 2022-05-13 at 14:06:11 -0700, Jordan Justen wrote:
> On 2022-05-13 05:31:00, Lionel Landwerlin wrote:
> > On 02/05/2022 17:15, Ramalingam C wrote:
> > > Capture the impact of memory region preference list of the objects, on
> > > their memory residency and Flat-CCS capability.
> > >
> > > v2:
> > >    Fix the Flat-CCS capability of an obj with {lmem, smem} preference
> > >    list [Thomas]
> > > v3:
> > >    Reworded the doc [Matt]
> > >
> > > Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> > > cc: Matthew Auld <matthew.auld@intel.com>
> > > cc: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
> > > cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > cc: Jon Bloomfield <jon.bloomfield@intel.com>
> > > cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> > > cc: Kenneth Graunke <kenneth@whitecape.org>
> > > cc: mesa-dev@lists.freedesktop.org
> > > cc: Jordan Justen <jordan.l.justen@intel.com>
> > > cc: Tony Ye <tony.ye@intel.com>
> > > Reviewed-by: Matthew Auld <matthew.auld@intel.com>
> > > ---
> > >   include/uapi/drm/i915_drm.h | 16 ++++++++++++++++
> > >   1 file changed, 16 insertions(+)
> > >
> > > diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> > > index a2def7b27009..b7e1c2fe08dc 100644
> > > --- a/include/uapi/drm/i915_drm.h
> > > +++ b/include/uapi/drm/i915_drm.h
> > > @@ -3443,6 +3443,22 @@ struct drm_i915_gem_create_ext {
> > >    * At which point we get the object handle in &drm_i915_gem_create_ext.handle,
> > >    * along with the final object size in &drm_i915_gem_create_ext.size, which
> > >    * should account for any rounding up, if required.
> > > + *
> > > + * Note that userspace has no means of knowing the current backing region
> > > + * for objects where @num_regions is larger than one. The kernel will only
> > > + * ensure that the priority order of the @regions array is honoured, either
> > > + * when initially placing the object, or when moving memory around due to
> > > + * memory pressure
> > > + *
> > > + * On Flat-CCS capable HW, compression is supported for the objects residing
> > > + * in I915_MEMORY_CLASS_DEVICE. When such objects (compressed) has other
> > > + * memory class in @regions and migrated (by I915, due to memory
> > > + * constrain) to the non I915_MEMORY_CLASS_DEVICE region, then I915 needs to
> > > + * decompress the content. But I915 dosen't have the required information to
> > > + * decompress the userspace compressed objects.
> > > + *
> > > + * So I915 supports Flat-CCS, only on the objects which can reside only on
> > > + * I915_MEMORY_CLASS_DEVICE regions.
> > 
> > I think it's fine to assume Flat-CSS surface will always be in lmem.
> > 
> > I see no issue for the Anv Vulkan driver.
> > 
> > Maybe Nanley or Ken can speak for the Iris GL driver?
> > 
> 
> Acked-by: Jordan Justen <jordan.l.justen@intel.com>
Thank you Jordan for the Ack!

Ram
> 
> I think Nanley has accounted for this on iris with:
> 
> https://gitlab.freedesktop.org/mesa/mesa/-/commit/42a865730ef72574e179b56a314f30fdccc6cba8
> 
> -Jordan