linux-kernel - Re: [Intel-gfx] [PATCH v5 2/5] drm/i915: enforce min GTT alignment for discrete cards

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Date:   Wed, 26 Jan 2022 16:45:22 +0100
From:   Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>
To:     Robert Beckett <bob.beckett@...labora.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Matthew Auld <matthew.auld@...el.com>
Subject: Re: [Intel-gfx] [PATCH v5 2/5] drm/i915: enforce min GTT alignment
 for discrete cards


On 1/25/22 20:35, Robert Beckett wrote:
> From: Matthew Auld <matthew.auld@...el.com>
>
> For local-memory objects we need to align the GTT addresses
> to 64K, both for the ppgtt and ggtt.
>
> We need to support vm->min_alignment > 4K, depending
> on the vm itself and the type of object we are inserting.
> With this in mind update the GTT selftests to take this
> into account.
>
> For compact-pt we further align and pad lmem object GTT addresses
> to 2MB to ensure PDEs contain consistent page sizes as
> required by the HW.
>
> v3:
> 	* use needs_compact_pt flag to discriminate between
> 	  64K and 64K with compact-pt
> 	* add i915_vm_obj_min_alignment
> 	* use i915_vm_obj_min_alignment to round up vma reservation
> 	  if compact-pt instead of hard coding
> v5:
> 	* fix i915_vm_obj_min_alignment for internal objects which
> 	  have no memory region
>
> Signed-off-by: Matthew Auld <matthew.auld@...el.com>
> Signed-off-by: Ramalingam C <ramalingam.c@...el.com>
> Signed-off-by: Robert Beckett <bob.beckett@...labora.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
> ---
>   .../i915/gem/selftests/i915_gem_client_blt.c  | 23 +++--
>   drivers/gpu/drm/i915/gt/intel_gtt.c           | 12 +++
>   drivers/gpu/drm/i915/gt/intel_gtt.h           | 18 ++++
>   drivers/gpu/drm/i915/i915_vma.c               |  9 ++
>   drivers/gpu/drm/i915/selftests/i915_gem_gtt.c | 96 ++++++++++++-------
>   5 files changed, 117 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_client_blt.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_client_blt.c
> index c8ff8bf0986d..f0bfce53258f 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_client_blt.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_client_blt.c
> @@ -39,6 +39,7 @@ struct tiled_blits {
>   	struct blit_buffer scratch;
>   	struct i915_vma *batch;
>   	u64 hole;
> +	u64 align;
>   	u32 width;
>   	u32 height;
>   };
> @@ -410,14 +411,21 @@ tiled_blits_create(struct intel_engine_cs *engine, struct rnd_state *prng)
>   		goto err_free;
>   	}
>   
> -	hole_size = 2 * PAGE_ALIGN(WIDTH * HEIGHT * 4);
> +	t->align = I915_GTT_PAGE_SIZE_2M; /* XXX worst case, derive from vm! */
> +	t->align = max(t->align,
> +		       i915_vm_min_alignment(t->ce->vm, INTEL_MEMORY_LOCAL));
> +	t->align = max(t->align,
> +		       i915_vm_min_alignment(t->ce->vm, INTEL_MEMORY_SYSTEM));

Don't we always end up with 2M here, regardless of the vm restrictions?