Re: [Intel-gfx] [PATCH v2 15/15] drm/i915/ttm: Add io sgt caching to i915_ttm_io_mem_pfn

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

On 5/18/21 10:27 AM, Thomas Hellström wrote:
> From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>
> Instead of walking the sg table manually, use our caching helpers
> to do the sgt caching. To prevent lifetime issues of ttm_bo vs
> i915_gem_object, we will use a separate member, instead of re-using
> the dma page member.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_object.h    |  6 +--
>   .../gpu/drm/i915/gem/i915_gem_object_types.h  |  1 +
>   drivers/gpu/drm/i915/gem/i915_gem_pages.c     |  3 +-
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c       | 46 ++++++++++---------
>   4 files changed, 30 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index a3ad8cf4eefd..ff59e6c640e6 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -342,14 +342,14 @@ struct scatterlist *
>   __i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
>   			 struct i915_gem_object_page_iter *iter,
>   			 unsigned int n,
> -			 unsigned int *offset, bool allow_alloc);
> +			 unsigned int *offset, bool allow_alloc, bool dma);
>   
>   static inline struct scatterlist *
>   i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
>   		       unsigned int n,
>   		       unsigned int *offset, bool allow_alloc)
>   {
> -	return __i915_gem_object_get_sg(obj, &obj->mm.get_page, n, offset, allow_alloc);
> +	return __i915_gem_object_get_sg(obj, &obj->mm.get_page, n, offset, allow_alloc, false);
>   }
>   
>   static inline struct scatterlist *
> @@ -357,7 +357,7 @@ i915_gem_object_get_sg_dma(struct drm_i915_gem_object *obj,
>   			   unsigned int n,
>   			   unsigned int *offset, bool allow_alloc)
>   {
> -	return __i915_gem_object_get_sg(obj, &obj->mm.get_dma_page, n, offset, allow_alloc);
> +	return __i915_gem_object_get_sg(obj, &obj->mm.get_dma_page, n, offset, allow_alloc, true);
>   }
>   
>   struct page *
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> index 31d828e91cf4..828310802b9f 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> @@ -324,6 +324,7 @@ struct drm_i915_gem_object {
>   
>   	struct {
>   		struct sg_table *cached_io_st;
> +		struct i915_gem_object_page_iter get_io_page;
>   	} ttm;
>   
>   	/** Record of address bit 17 of each page at last unbind. */
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> index 62ee2185a41b..577352b4f2f6 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> @@ -465,9 +465,8 @@ __i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
>   			 struct i915_gem_object_page_iter *iter,
>   			 unsigned int n,
>   			 unsigned int *offset,
> -			 bool allow_alloc)
> +			 bool allow_alloc, bool dma)
>   {
> -	const bool dma = iter == &obj->mm.get_dma_page;
>   	struct scatterlist *sg;
>   	unsigned int idx, count;
>   
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index fe9ac50b2470..1eaefb89e859 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -167,11 +167,20 @@ static int i915_ttm_move_notify(struct ttm_buffer_object *bo)
>   
>   static void i915_ttm_free_cached_io_st(struct drm_i915_gem_object *obj)
>   {
> -	if (obj->ttm.cached_io_st) {
> -		sg_free_table(obj->ttm.cached_io_st);
> -		kfree(obj->ttm.cached_io_st);
> -		obj->ttm.cached_io_st = NULL;
> -	}
> +	struct radix_tree_iter iter;
> +	void __rcu **slot;
> +
> +	if (!obj->ttm.cached_io_st)
> +		return;
> +
> +	rcu_read_lock();
> +	radix_tree_for_each_slot(slot, &obj->ttm.get_io_page.radix, &iter, 0)
> +		radix_tree_delete(&obj->ttm.get_io_page.radix, iter.index);
> +	rcu_read_unlock();
> +
> +	sg_free_table(obj->ttm.cached_io_st);
> +	kfree(obj->ttm.cached_io_st);
> +	obj->ttm.cached_io_st = NULL;
>   }
>   
>   static void i915_ttm_purge(struct drm_i915_gem_object *obj)
> @@ -340,8 +349,11 @@ static int i915_ttm_move(struct ttm_buffer_object *bo, bool evict,
>   	i915_ttm_move_memcpy(bo, new_mem, new_iter, old_iter);
>   	i915_ttm_free_cached_io_st(obj);
>   
> -	if (!new_man->use_tt)
> +	if (!new_man->use_tt) {
>   		obj->ttm.cached_io_st = new_st;
> +		obj->ttm.get_io_page.sg_pos = new_st->sgl;
> +		obj->ttm.get_io_page.sg_idx = 0;
> +	}
>   
>   	return 0;
>   }
> @@ -362,26 +374,15 @@ static unsigned long i915_ttm_io_mem_pfn(struct ttm_buffer_object *bo,
>   					 unsigned long page_offset)
>   {
>   	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
> -	struct sg_table *sgt = obj->ttm.cached_io_st;
> +	unsigned long base = obj->mm.region->iomap.base - obj->mm.region->region.start;
>   	struct scatterlist *sg;
> -	unsigned int i;
> +	unsigned int ofs;
>   
>   	GEM_WARN_ON(bo->ttm);
>   
> -	for_each_sgtable_dma_sg(sgt, sg, i) {
> -		unsigned long sg_max = sg->length >> PAGE_SHIFT;
> +	sg = __i915_gem_object_get_sg(obj, &obj->ttm.get_io_page, page_offset, &ofs, true, true);
>   
> -		if (page_offset < sg_max) {
> -			unsigned long base =
> -				obj->mm.region->iomap.base - obj->mm.region->region.start;
> -
> -			return ((base + sg_dma_address(sg)) >> PAGE_SHIFT) + page_offset;
> -		}
> -
> -		page_offset -= sg_max;
> -	}
> -	GEM_BUG_ON(1);
> -	return 0;
> +	return ((base + sg_dma_address(sg)) >> PAGE_SHIFT) + ofs;
>   }
>   
>   struct ttm_device_funcs i915_ttm_bo_driver = {
> @@ -613,6 +614,9 @@ int __i915_gem_ttm_object_init(struct intel_memory_region *mem,
>   	obj->read_domains = I915_GEM_DOMAIN_WC | I915_GEM_DOMAIN_GTT;
>   	i915_gem_object_set_cache_coherency(obj, I915_CACHE_NONE);
>   
> +	INIT_RADIX_TREE(&obj->ttm.get_io_page.radix, GFP_KERNEL | __GFP_NOWARN);
> +	mutex_init(&obj->ttm.get_io_page.lock);
> +

Perhaps a mutex_destroy() in error path and destructor for full 
debugging purposes?

Otherwise LGTM,

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>


>   	ret = ttm_bo_init(&i915->bdev, i915_gem_to_ttm(obj), size,
>   			  ttm_bo_type_kernel, &i915_sys_placement, alignment,
>   			  true, NULL, NULL, i915_ttm_bo_destroy);
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