Re: [PATCH v3 12/15] drm/i915/create: apply ALLOC_GPU_ONLY by default

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On 2/11/22 12:34, Matthew Auld wrote:
> Starting from DG2+, when dealing with LMEM, we assume that by default
> all userspace allocations should be placed in the non-mappable portion
> of LMEM.  Note that dumb buffers are not included here, since these are
> not "GPU accelerated" and likely need CPU access. We choose to just
> always set GPU_ONLY, and let the backend figure out if that should be
> ignored on discrete devices.
>
> In a later patch userspace will be able to provide a hint if CPU access
> to the buffer is needed.
>
> v2(Thomas)
>   - Apply GPU_ONLY on all discrete devices, but only if the BO can be
>     placed in LMEM. Down in the depths this should be turned into a noop,
>     where required, and as an annotation it still make some sense. If we
>     apply it regardless of the placements then we end up needing to check
>     the placements during exec capture. Also it's slightly inconsistent
>     since the NEEDS_CPU_ACCESS can only be applied on objects that can be
>     placed in LMEM. The other annoyance would be gem_create_ext vs plain
>     gem_create, if we were to always apply GPU_ONLY.
>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Jon Bloomfield <jon.bloomfield@intel.com>

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>


> ---
>   drivers/gpu/drm/i915/gem/i915_gem_create.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> index 9402d4bf4ffc..ecb8c2feec46 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> @@ -424,6 +424,14 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
>   		ext_data.n_placements = 1;
>   	}
>   
> +	/*
> +	 * TODO: add a userspace hint to force CPU_ACCESS for the object, which
> +	 * can override this.
> +	 */
> +	if (ext_data.n_placements > 1 ||
> +	    ext_data.placements[0]->type != INTEL_MEMORY_SYSTEM)
> +		ext_data.flags |= I915_BO_ALLOC_GPU_ONLY;
> +
>   	obj = __i915_gem_object_create_user_ext(i915, args->size,
>   						ext_data.placements,
>   						ext_data.n_placements,