[Intel-gfx] [PATCH v4] drm/i915: Add soft-pinning API for execbuffer

[Chris Wilson]

On Wed, Jul 15, 2015 at 08:25:23PM +0530, Goel, Akash wrote:
> >>+int
> >>+i915_gem_evict_for_vma(struct i915_vma *target)
> >>+{
> >>+	struct drm_mm_node *node, *next;
> >>+
> >>+	list_for_each_entry_safe(node, next,
> >>+			&target->vm->mm.head_node.node_list,
> >>+			node_list) {
> >>+		struct i915_vma *vma;
> >>+		int ret;
> >>+
> >>+		if (node->start + node->size <= target->node.start)
> >>+			continue;
> >>+		if (node->start >= target->node.start + target->node.size)
> >>+			break;
> >>+
> >>+		vma = container_of(node, typeof(*vma), node);
> >>+
> >>+		if (vma->pin_count) {
> >>+			/* We may need to evict a buffer in the same batch */
> >>+			if (!vma->exec_entry)
> >>+				return -EBUSY;
> >>+
> >>+			if (vma->exec_entry->flags & EXEC_OBJECT_PINNED)
> >>+				/* Overlapping fixed objects in the same batch
> >>*/
> >>+				return -EINVAL;
> >>+
> >>+			return -ENOSPC;
> 
> Can we actually hit this condition, considering the soft pinned
> objects are now on the front side of 'eb->vmas' list ?
> If we do encounter such a case, it probably means that the
> overlapping object is already pinned from some other path.

Note that softpinned objects are only first on the second pass through
the reservation.
 
> Is there a scope of an additional check here ?
> i.e. if (vma->pin_count) is > 1, this indicates that the object is
> not only pinned due to execbuffer, hence cannot be evicted, so
> -EBUSY can be straight away returned to User.

Consider this instead:

int
i915_gem_evict_for_vma(struct i915_vma *target, unsigned flags)
{
        struct list_head eviction_list;
        struct interval_tree_node *it;
        u64 end = target->node.start + target->node.size;
        struct drm_mm_node *node;
        struct i915_vma *vma, *next;
        int ret;

        it = interval_tree_iter_first(&target->vm->mm.interval_tree,
                                      target->node.start, end -1);
        if (it == NULL)
                return 0;

        INIT_LIST_HEAD(&eviction_list);
        node = container_of(it, typeof(*node), it);
        list_for_each_entry_from(node,
                                 &target->vm->mm.head_node.node_list,
                                 node_list) {
                if (node->start >= end)
                        break;

                vma = container_of(node, typeof(*vma), node);
                if (flags & PIN_NONBLOCK &&
                    (vma->pin_count || vma->active.request)) {
                        ret = -ENOSPC;
                        break;
                }

                if (vma->exec_entry &&
                    vma->exec_entry->flags & EXEC_OBJECT_PINNED) {
                        /* Overlapping pinned objects in the same batch */
                        ret = -EINVAL;
                        break;
                }

                if (vma->pin_count) {
                        /* We may need to evict an buffer in the same batch */
                        ret = vma->exec_entry ? -ENOSPC : -EBUSY;
                        break;
                }

                list_add(&vma->exec_list, &eviction_list);
                drm_gem_object_reference(&vma->obj->base);
        }

        ret = 0;
        list_for_each_entry_safe(vma, next, &eviction_list, exec_list) {
                struct drm_i915_gem_object *obj = vma->obj;
                if (ret == 0)
                        ret = i915_vma_unbind(vma);
                drm_gem_object_unreference(&obj->base);
        }

        return ret;
}
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre