[PATCH] drm/amdgpu: restructure amdgpu_vram_mgr_new

[Felix Kuehling]

Am 2021-04-26 um 4:54 a.m. schrieb Christian König:
> Merge the two loops, loosen the restriction for big allocations.
> This reduces the CPU overhead in the good case, but increases
> it a bit under memory pressure.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 58 +++++++++-----------
>  1 file changed, 27 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> index 529c5c32a205..e2cbe19404c0 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> @@ -358,13 +358,13 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>  			       const struct ttm_place *place,
>  			       struct ttm_resource *mem)
>  {
> +	unsigned long lpfn, num_nodes, pages_per_node, 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;
>  	struct drm_mm *mm = &mgr->mm;
> -	struct drm_mm_node *nodes;
>  	enum drm_mm_insert_mode mode;
> -	unsigned long lpfn, num_nodes, pages_per_node, pages_left;
> -	uint64_t vis_usage = 0, mem_bytes, max_bytes;
> +	struct drm_mm_node *nodes;
>  	unsigned i;
>  	int r;
>  
> @@ -391,9 +391,10 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>  		pages_per_node = HPAGE_PMD_NR;
>  #else
>  		/* default to 2MB */
> -		pages_per_node = (2UL << (20UL - PAGE_SHIFT));
> +		pages_per_node = 2UL << (20UL - PAGE_SHIFT);
>  #endif
> -		pages_per_node = max((uint32_t)pages_per_node, mem->page_alignment);
> +		pages_per_node = max_t(uint32_t, pages_per_node,
> +				       mem->page_alignment);
>  		num_nodes = DIV_ROUND_UP(mem->num_pages, pages_per_node);
>  	}
>  
> @@ -411,42 +412,37 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>  	mem->start = 0;
>  	pages_left = mem->num_pages;
>  
> -	spin_lock(&mgr->lock);
> -	for (i = 0; pages_left >= pages_per_node; ++i) {
> -		unsigned long pages = rounddown_pow_of_two(pages_left);
> -
> -		/* Limit maximum size to 2GB due to SG table limitations */
> -		pages = min(pages, (2UL << (30 - PAGE_SHIFT)));
> +	/* Limit maximum size to 2GB due to SG table limitations */
> +	pages = min(pages_left, 2UL << (30 - PAGE_SHIFT));
>  
> -		r = drm_mm_insert_node_in_range(mm, &nodes[i], pages,
> -						pages_per_node, 0,
> -						place->fpfn, lpfn,
> -						mode);
> -		if (unlikely(r))
> -			break;
> -
> -		vis_usage += amdgpu_vram_mgr_vis_size(adev, &nodes[i]);
> -		amdgpu_vram_mgr_virt_start(mem, &nodes[i]);
> -		pages_left -= pages;
> -	}
> -
> -	for (; pages_left; ++i) {
> -		unsigned long pages = min(pages_left, pages_per_node);
> +	i = 0;
> +	spin_lock(&mgr->lock);
> +	while (pages_left) {
>  		uint32_t alignment = mem->page_alignment;
>  
> -		if (pages == pages_per_node)
> +		if (pages >= pages_per_node)
>  			alignment = pages_per_node;
>  
> -		r = drm_mm_insert_node_in_range(mm, &nodes[i],
> -						pages, alignment, 0,
> -						place->fpfn, lpfn,
> -						mode);
> -		if (unlikely(r))
> +		r = drm_mm_insert_node_in_range(mm, &nodes[i], pages, alignment,
> +						0, place->fpfn, lpfn, mode);
> +		if (unlikely(r)) {
> +			if (pages > pages_per_node) {

This means we can never allocate chunks smaller than 2MB, except for the
tail. And the tail still needs to be allocated in one piece if it's < 2MB.

On the other hand, we should not allow allocations smaller than
mem->page_alignment, except for the tail. So should this condition be
"if (pages > mem->page_alignment)" to allow maximum flexibility for
allocations without physical alignment constraints when memory is very
fragmented?

Regards,
  Felix


> +				if (is_power_of_2(pages))
> +					pages = pages / 2;
> +				else
> +					pages = rounddown_pow_of_two(pages);
> +				continue;
> +			}
>  			goto error;
> +		}
>  
>  		vis_usage += amdgpu_vram_mgr_vis_size(adev, &nodes[i]);
>  		amdgpu_vram_mgr_virt_start(mem, &nodes[i]);
>  		pages_left -= pages;
> +		++i;
> +
> +		if (pages > pages_left)
> +			pages = pages_left;
>  	}
>  	spin_unlock(&mgr->lock);
>