On 12/10/15 11:10, Chris Wilson wrote:
On Mon, Oct 12, 2015 at 10:31:35AM +0100, Chris Wilson wrote:
We basically need to clone the obj, move the pages and vma over and so
as the vma die the pages are unreferenced. All new use will be forced to
call gup and be fine.
Ok, that smells ok, I'll see how doable that is.
Hmm. If we take the vma-centric driver as granted (i.e. using the vma as the
token when pinning, the vma holds fences etc), the tricky part if that we
don't hold a reference from the pinned vma to the object. pin_display to
the rescue!
Initial sketch:
static struct drm_i915_gem_object *steal_pages(struct drm_i915_gem_object *obj)
{
struct drm_i915_gem_object *clone;
struct i915_vma *vma;
int i;
BUG_ON(obj->stolen);
clone = i915_gem_object_alloc(obj->base.dev);
if (clone == NULL)
return clone;
drm_gem_private_object_init(obj->base.dev,
&clone->base,
obj->base.size);
i915_gem_object_init(clone, obj->ops);
list_splice_init(&obj->vma_list, &clone->vma_list);
list_for_each_entry(vma, &clone->vma_list, obj_link)
vma->obj = clone;
if (obj->pin_display) {
clone->pin_display = obj->pin_display;
while (obj->pin_display--) {
drm_gem_object_reference(&clone->base);
drm_gem_object_unreference(&obj->base);
}
}
clone->bind_count = obj->bind_count;
obj->bind_count = 0;
/* vma_ht / vma_hashed */
for (i = 0; i < I915_NUM_RINGS; i++) {
if (obj->last_read[i].request == NULL)
continue;
clone->last_read[i].request = obj->last_read[i].request;
list_replace_init(&obj->last_read[i].link,
&clone->last_read[i].link);
clone->flags |= 1 << (i + I915_BO_ACTIVE_SHIFT);
}
if (obj->last_write.request) {
clone->last_write.request = obj->last_write.request;
list_replace_init(&obj->last_write.link,
&clone->last_write.link);
}
clone->dirty = obj->dirty;
obj->dirty = false;
clone->tiling_mode = obj->tiling_mode;
clone->stride = obj->stride;
clone->pin_display = obj->pin_display;
obj->pin_display = 0;
clone->madv = I915_MADV_DONTNEED;
clone->pages = obj->pages;
clone->pages_pin_count = obj->pages_pin_count;
clone->get_page = obj->get_page;
clone->vmapping = obj->vmapping;
obj->pages = NULL;
obj->pages_pin_count = 0;
obj->vmapping = NULL;
clone->bit_17 = obj->bit_17;
obj->bit_17 = NULL;
i915_gem_release_mmap(obj);
if (I915_BO_IS_ACTIVE(clone))
clone->active_reference = true;
else
drm_gem_object_unreference(&clone->base);
return clone;
}
It does have the presumption that we have either an active reference or a
pinned reference.
I get the general idea but the base is too far from the current code to
properly evaluate. But in principle it sounds promising.
Regards,
Tvrtko
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