[Intel-gfx] [PATCH] drm/i915: Skip unbinding large unmappable global buffers

[Tvrtko Ursulin]

On 13/10/2016 09:55, Chris Wilson wrote:
> If the user requests a mappable binding to the global GTT, we will first
> unbind an existing mapping if it doesn't match. We will unbind even if
> there is no possibility that the object can fit in the mappable
> aperture. This may lead to a ping-pong migration of the object, for
> example igt/gem_exec_big.
>
> Testcase: igt/gem_exec_big
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 19 ++++++++++++++++++-
>   1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 2f939f90984b..f33aa9bb95c0 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3144,6 +3144,9 @@ search_free:
>   
>   			goto err_unpin;
>   		}
> +
> +		GEM_BUG_ON(vma->node.start < start);
> +		GEM_BUG_ON(vma->node.start + vma->node.size > end);
>   	}
>   	GEM_BUG_ON(!i915_gem_valid_gtt_space(vma, obj->cache_level));
>   
> @@ -3843,7 +3846,8 @@ i915_gem_object_ggtt_pin(struct drm_i915_gem_object *obj,
>   			 u64 alignment,
>   			 u64 flags)
>   {
> -	struct i915_address_space *vm = &to_i915(obj->base.dev)->ggtt.base;
> +	struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
> +	struct i915_address_space *vm = &dev_priv->ggtt.base;
>   	struct i915_vma *vma;
>   	int ret;
>   
> @@ -3858,6 +3862,19 @@ i915_gem_object_ggtt_pin(struct drm_i915_gem_object *obj,
>   		    (i915_vma_is_pinned(vma) || i915_vma_is_active(vma)))
>   			return ERR_PTR(-ENOSPC);
>   
> +		if (flags & PIN_MAPPABLE) {
> +			u32 fence_size;
> +
> +			fence_size = i915_gem_get_ggtt_size(dev_priv, vma->size,
> +							    i915_gem_object_get_tiling(obj));
> +			if (fence_size > dev_priv->ggtt.mappable_end)
> +				return ERR_PTR(-E2BIG);
> +
> +			if (flags & PIN_NONBLOCK &&
> +			    fence_size > dev_priv->ggtt.mappable_end / 2)
> +				return ERR_PTR(-ENOSPC);

One half of aperture is a magic number or something else?

Regards,

Tvrtko

> +		}
> +
>   		WARN(i915_vma_is_pinned(vma),
>   		     "bo is already pinned in ggtt with incorrect alignment:"
>   		     " offset=%08x, req.alignment=%llx,"