[PATCH] drm/amdgpu: further lower VRAM allocation overhead

[Eric Huang]

Hi Christian/Felix,

If you don't have objection, it will be pushed into 
amd-staging-dkms-5.11 and amd-staging-drm-next.

Thanks,
Eric

On 2021-07-13 3:17 p.m., Eric Huang wrote:
> For allocations larger than 48MiB we need more than a page for the
> housekeeping in the worst case resulting in the usual vmalloc overhead.
>
> Try to avoid this by assuming the good case and only falling back to the
> worst case if this didn't worked.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Signed-off-by: Eric Huang <jinhuieric.huang at amd.com>
> Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 71 +++++++++++++++-----
>   1 file changed, 53 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> index be4261c4512e..ecbe05e1db66 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> @@ -361,9 +361,11 @@ static void amdgpu_vram_mgr_virt_start(struct ttm_resource *mem,
>   static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>   			       struct ttm_buffer_object *tbo,
>   			       const struct ttm_place *place,
> +			       unsigned long num_nodes,
> +			       unsigned long pages_per_node,
>   			       struct ttm_resource *mem)
>   {
> -	unsigned long lpfn, num_nodes, pages_per_node, pages_left, pages;
> +	unsigned long lpfn, pages_left, pages;
>   	struct amdgpu_vram_mgr *mgr = to_vram_mgr(man);
>   	struct amdgpu_device *adev = to_amdgpu_device(mgr);
>   	uint64_t vis_usage = 0, mem_bytes, max_bytes;
> @@ -393,21 +395,6 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>   		return -ENOSPC;
>   	}
>   
> -	if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
> -		pages_per_node = ~0ul;
> -		num_nodes = 1;
> -	} else {
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -		pages_per_node = HPAGE_PMD_NR;
> -#else
> -		/* default to 2MB */
> -		pages_per_node = 2UL << (20UL - PAGE_SHIFT);
> -#endif
> -		pages_per_node = max_t(uint32_t, pages_per_node,
> -				       mem->page_alignment);
> -		num_nodes = DIV_ROUND_UP(mem->num_pages, pages_per_node);
> -	}
> -
>   	nodes = kvmalloc_array((uint32_t)num_nodes, sizeof(*nodes),
>   			       GFP_KERNEL | __GFP_ZERO);
>   	if (!nodes) {
> @@ -435,7 +422,12 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>   	i = 0;
>   	spin_lock(&mgr->lock);
>   	while (pages_left) {
> -		uint32_t alignment = mem->page_alignment;
> +		unsigned long alignment = mem->page_alignment;
> +
> +		if (i >= num_nodes) {
> +			r = -E2BIG;
> +			goto error;
> +		}
>   
>   		if (pages >= pages_per_node)
>   			alignment = pages_per_node;
> @@ -492,6 +484,49 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>   	return r;
>   }
>   
> +/**
> + * amdgpu_vram_mgr_alloc - allocate new range
> + *
> + * @man: TTM memory type manager
> + * @tbo: TTM BO we need this range for
> + * @place: placement flags and restrictions
> + * @mem: the resulting mem object
> + *
> + * Allocate VRAM for the given BO.
> + */
> +static int amdgpu_vram_mgr_alloc(struct ttm_resource_manager *man,
> +				 struct ttm_buffer_object *tbo,
> +				 const struct ttm_place *place,
> +				 struct ttm_resource *mem)
> +{
> +	unsigned long num_nodes, pages_per_node;
> +	int r;
> +
> +	if (place->flags & TTM_PL_FLAG_CONTIGUOUS)
> +		return amdgpu_vram_mgr_new(man, tbo, place, 1, ~0ul, mem);
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	pages_per_node = HPAGE_PMD_NR;
> +#else
> +	/* default to 2MB */
> +	pages_per_node = 2UL << (20UL - PAGE_SHIFT);
> +#endif
> +	pages_per_node = max_t(uint32_t, pages_per_node,
> +			       mem->page_alignment);
> +	num_nodes = DIV_ROUND_UP(mem->num_pages, pages_per_node);
> +
> +	if (sizeof(struct drm_mm_node) * num_nodes > PAGE_SIZE) {
> +		r = amdgpu_vram_mgr_new(man, tbo, place,
> +				PAGE_SIZE / sizeof(struct drm_mm_node),
> +				pages_per_node,	mem);
> +		if (r != -E2BIG)
> +			return r;
> +	}
> +
> +	return amdgpu_vram_mgr_new(man, tbo, place, num_nodes, pages_per_node,
> +				   mem);
> +}
> +
>   /**
>    * amdgpu_vram_mgr_del - free ranges
>    *
> @@ -693,7 +728,7 @@ static void amdgpu_vram_mgr_debug(struct ttm_resource_manager *man,
>   }
>   
>   static const struct ttm_resource_manager_func amdgpu_vram_mgr_func = {
> -	.alloc	= amdgpu_vram_mgr_new,
> +	.alloc	= amdgpu_vram_mgr_alloc,
>   	.free	= amdgpu_vram_mgr_del,
>   	.debug	= amdgpu_vram_mgr_debug
>   };