Re: [PATCH 2/6] drm/i915: Tidy batch pool logic

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

Hi,

Tidy is small understatement but OK.. :) inline..

On 03/09/2015 09:55 AM, Chris Wilson wrote:
> Move the madvise logic out of the execbuffer main path into the
> relatively rare allocation path, making the execbuffer manipulation less
> fragile.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_cmd_parser.c     | 12 +++------
>   drivers/gpu/drm/i915/i915_gem_batch_pool.c | 39 +++++++++++++++---------------
>   drivers/gpu/drm/i915/i915_gem_execbuffer.c | 13 ++++------
>   3 files changed, 27 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
> index 9a6da3536ae5..3e5e8cb54a88 100644
> --- a/drivers/gpu/drm/i915/i915_cmd_parser.c
> +++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
> @@ -866,6 +866,9 @@ static u32 *copy_batch(struct drm_i915_gem_object *dest_obj,
>   	    batch_len + batch_start_offset > src_obj->base.size)
>   		return ERR_PTR(-E2BIG);
>
> +	if (WARN_ON(dest_obj->pages_pin_count == 0))
> +		return ERR_PTR(-ENODEV);
> +
>   	ret = i915_gem_obj_prepare_shmem_read(src_obj, &needs_clflush);
>   	if (ret) {
>   		DRM_DEBUG_DRIVER("CMD: failed to prepare shadow batch\n");
> @@ -879,13 +882,6 @@ static u32 *copy_batch(struct drm_i915_gem_object *dest_obj,
>   		goto unpin_src;
>   	}
>
> -	ret = i915_gem_object_get_pages(dest_obj);
> -	if (ret) {
> -		DRM_DEBUG_DRIVER("CMD: Failed to get pages for shadow batch\n");
> -		goto unmap_src;
> -	}
> -	i915_gem_object_pin_pages(dest_obj);
> -
>   	ret = i915_gem_object_set_to_cpu_domain(dest_obj, true);
>   	if (ret) {
>   		DRM_DEBUG_DRIVER("CMD: Failed to set shadow batch to CPU\n");
> @@ -895,7 +891,6 @@ static u32 *copy_batch(struct drm_i915_gem_object *dest_obj,
>   	dst = vmap_batch(dest_obj, 0, batch_len);
>   	if (!dst) {
>   		DRM_DEBUG_DRIVER("CMD: Failed to vmap shadow batch\n");
> -		i915_gem_object_unpin_pages(dest_obj);
>   		ret = -ENOMEM;
>   		goto unmap_src;
>   	}

My tree, or maybe the current tree, has another unpin under unpin_src 
label, so perhaps you'll need to rebase?

> @@ -1126,7 +1121,6 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
>   	}
>
>   	vunmap(batch_base);
> -	i915_gem_object_unpin_pages(shadow_batch_obj);
>
>   	return ret;
>   }
> diff --git a/drivers/gpu/drm/i915/i915_gem_batch_pool.c b/drivers/gpu/drm/i915/i915_gem_batch_pool.c
> index 564be7c5ea7e..21f3356cc0ab 100644
> --- a/drivers/gpu/drm/i915/i915_gem_batch_pool.c
> +++ b/drivers/gpu/drm/i915/i915_gem_batch_pool.c
> @@ -67,25 +67,23 @@ void i915_gem_batch_pool_fini(struct i915_gem_batch_pool *pool)
>   					 struct drm_i915_gem_object,
>   					 batch_pool_list);
>
> -		WARN_ON(obj->active);
> -
> -		list_del_init(&obj->batch_pool_list);
> +		list_del(&obj->batch_pool_list);
>   		drm_gem_object_unreference(&obj->base);
>   	}
>   }
>
>   /**
> - * i915_gem_batch_pool_get() - select a buffer from the pool
> + * i915_gem_batch_pool_get() - allocate a buffer from the pool
>    * @pool: the batch buffer pool
>    * @size: the minimum desired size of the returned buffer
>    *
> - * Finds or allocates a batch buffer in the pool with at least the requested
> - * size. The caller is responsible for any domain, active/inactive, or
> - * purgeability management for the returned buffer.
> + * Returns an inactive buffer from @pool with at least @size bytes,
> + * with the pages pinned. The caller must i915_gem_object_unpin_pages()
> + * on the returned object.
>    *
>    * Note: Callers must hold the struct_mutex
>    *
> - * Return: the selected batch buffer object
> + * Return: the buffer object or an error pointer
>    */
>   struct drm_i915_gem_object *
>   i915_gem_batch_pool_get(struct i915_gem_batch_pool *pool,
> @@ -97,8 +95,7 @@ i915_gem_batch_pool_get(struct i915_gem_batch_pool *pool,
>   	WARN_ON(!mutex_is_locked(&pool->dev->struct_mutex));
>
>   	list_for_each_entry_safe(tmp, next,
> -			&pool->cache_list, batch_pool_list) {
> -
> +				 &pool->cache_list, batch_pool_list) {
>   		if (tmp->active)
>   			continue;
>
> @@ -114,25 +111,27 @@ i915_gem_batch_pool_get(struct i915_gem_batch_pool *pool,
>   		 * but not 'too much' bigger. A better way to do this
>   		 * might be to bucket the pool objects based on size.
>   		 */
> -		if (tmp->base.size >= size &&
> -		    tmp->base.size <= (2 * size)) {
> +		if (tmp->base.size >= size && tmp->base.size <= 2 * size) {
>   			obj = tmp;
>   			break;
>   		}
>   	}
>
> -	if (!obj) {
> +	if (obj == NULL) {
> +		int ret;
> +
>   		obj = i915_gem_alloc_object(pool->dev, size);
> -		if (!obj)
> +		if (obj == NULL)
>   			return ERR_PTR(-ENOMEM);
>
> -		list_add_tail(&obj->batch_pool_list, &pool->cache_list);
> -	}
> -	else
> -		/* Keep list in LRU order */
> -		list_move_tail(&obj->batch_pool_list, &pool->cache_list);
> +		ret = i915_gem_object_get_pages(obj);
> +		if (ret)
> +			return ERR_PTR(ret);
>
> -	obj->madv = I915_MADV_WILLNEED;
> +		obj->madv = I915_MADV_DONTNEED;
> +	}
>
> +	list_move_tail(&obj->batch_pool_list, &pool->cache_list);
> +	i915_gem_object_pin_pages(obj);
>   	return obj;
>   }
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index 58537079d3d7..36f8f05928d1 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -37,7 +37,6 @@
>   #define  __EXEC_OBJECT_HAS_FENCE (1<<30)
>   #define  __EXEC_OBJECT_NEEDS_MAP (1<<29)
>   #define  __EXEC_OBJECT_NEEDS_BIAS (1<<28)
> -#define  __EXEC_OBJECT_PURGEABLE (1<<27)
>
>   #define BATCH_OFFSET_BIAS (256*1024)
>
> @@ -224,12 +223,7 @@ i915_gem_execbuffer_unreserve_vma(struct i915_vma *vma)
>   	if (entry->flags & __EXEC_OBJECT_HAS_PIN)
>   		vma->pin_count--;
>
> -	if (entry->flags & __EXEC_OBJECT_PURGEABLE)
> -		obj->madv = I915_MADV_DONTNEED;
> -
> -	entry->flags &= ~(__EXEC_OBJECT_HAS_FENCE |
> -			  __EXEC_OBJECT_HAS_PIN |
> -			  __EXEC_OBJECT_PURGEABLE);
> +	entry->flags &= ~(__EXEC_OBJECT_HAS_FENCE | __EXEC_OBJECT_HAS_PIN);
>   }
>
>   static void eb_destroy(struct eb_vmas *eb)
> @@ -1181,11 +1175,13 @@ i915_gem_execbuffer_parse(struct intel_engine_cs *ring,
>   	if (ret)
>   		goto err;
>
> +	i915_gem_object_unpin_pages(shadow_batch_obj);
> +
>   	memset(shadow_exec_entry, 0, sizeof(*shadow_exec_entry));
>
>   	vma = i915_gem_obj_to_ggtt(shadow_batch_obj);
>   	vma->exec_entry = shadow_exec_entry;
> -	vma->exec_entry->flags = __EXEC_OBJECT_PURGEABLE | __EXEC_OBJECT_HAS_PIN;
> +	vma->exec_entry->flags = __EXEC_OBJECT_HAS_PIN;
>   	drm_gem_object_reference(&shadow_batch_obj->base);
>   	list_add_tail(&vma->exec_list, &eb->vmas);
>
> @@ -1194,6 +1190,7 @@ i915_gem_execbuffer_parse(struct intel_engine_cs *ring,
>   	return shadow_batch_obj;
>
>   err:
> +	i915_gem_object_unpin_pages(shadow_batch_obj);
>   	if (ret == -EACCES) /* unhandled chained batch */
>   		return batch_obj;
>   	else
>

Lets see if I got it right: By making the returned object pinned and 
having the caller unpin when done with it, it now can always be in 
"dontneed" state, and will be a shrinker candidate only (or as soon) 
when it is unpinned, correct?

I just don't get at the moment, if previously there was some race or bad 
interaction with less pinning and that signaling using 
_EXEC_OBJECT_PURGEABLE?

Regards,

Tvrtko

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