Re: [PATCH 16/20] drm/i915/create: apply ALLOC_TOPDOWN by default

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

On 1/26/22 16:21, 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.
>
> In a later patch userspace will be able to provide a hint if CPU access
> to the buffer is needed.
>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_create.c | 9 +++++++++
>   1 file changed, 9 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..e7456443f163 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> @@ -424,6 +424,15 @@ 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 (!IS_DG1(i915) && (ext_data.n_placements > 1 ||
> +			      ext_data.placements[0]->type !=
> +			      INTEL_MEMORY_SYSTEM))
> +		ext_data.flags |= I915_BO_ALLOC_TOPDOWN;

Perhaps we should include DG1 here as well, so that the same paths are 
taken regardless whether this is only a test on DG1?




> +
>   	obj = __i915_gem_object_create_user_ext(i915, args->size,
>   						ext_data.placements,
>   						ext_data.n_placements,