On 04/01/2022 12:51, Thomas Hellström wrote:
Implement async (non-blocking) unbinding by not syncing the vma before
calling unbind on the vma_resource.
Add the resulting unbind fence to the object's dma_resv from where it is
picked up by the ttm migration code.
Ideally these unbind fences should be coalesced with the migration blit
fence to avoid stalling the migration blit waiting for unbind, as they
can certainly go on in parallel, but since we don't yet have a
reasonable data structure to use to coalesce fences and attach the
resulting fence to a timeline, we defer that for now.
Note that with async unbinding, even while the unbind waits for the
preceding bind to complete before unbinding, the vma itself might have been
destroyed in the process, clearing the vma pages. Therefore we can
only allow async unbinding if we have a refcounted sg-list and keep a
refcount on that for the vma resource pages to stay intact until
binding occurs. If this condition is not met, a request for an async
unbind is diverted to a sync unbind.
v2:
- Use a separate kmem_cache for vma resources for now to isolate their
memory allocation and aid debugging.
- Move the check for vm closed to the actual unbinding thread. Regardless
of whether the vm is closed, we need the unbind fence to properly wait
for capture.
- Clear vma_res::vm on unbind and update its documentation.
v4:
- Take cache coloring into account when searching for vma resources
pending unbind. (Matthew Auld)
v5:
- Fix timeout and error check in i915_vma_resource_bind_dep_await().
- Avoid taking a reference on the object for async binding if
async unbind capable.
- Fix braces around a single-line if statement.
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
<snip>
@@ -434,12 +439,30 @@ int i915_vma_bind(struct i915_vma *vma,
bind_flags &= ~vma_flags;
if (bind_flags == 0) {
- kfree(vma_res);
+ i915_vma_resource_free(vma_res);
return 0;
}
GEM_BUG_ON(!atomic_read(&vma->pages_count));
+ /* Wait for or await async unbinds touching our range */
+ if (work && bind_flags & vma->vm->bind_async_flags)
+ ret = i915_vma_resource_bind_dep_await(vma->vm,
+ &work->base.chain,
+ vma->node.start,
+ vma->node.size,
+ true,
+ GFP_NOWAIT |
+ __GFP_RETRY_MAYFAIL |
+ __GFP_NOWARN);
+ else
+ ret = i915_vma_resource_bind_dep_sync(vma->vm, vma->node.start,
+ vma->node.size, true);
+ if (ret) {
+ i915_vma_resource_free(vma_res);
+ return ret;
+ }
+
if (vma->resource || !vma_res) {
/* Rebinding with an additional I915_VMA_*_BIND */
GEM_WARN_ON(!vma_flags);
@@ -452,9 +475,11 @@ int i915_vma_bind(struct i915_vma *vma,
if (work && bind_flags & vma->vm->bind_async_flags) {
struct dma_fence *prev;
- work->vma = vma;
+ work->vma_res = i915_vma_resource_get(vma->resource);
work->cache_level = cache_level;
work->flags = bind_flags;
+ if (vma->obj->mm.rsgt)
+ work->rsgt = i915_refct_sgt_get(vma->obj->mm.rsgt);
Hmmm, at a glance I would have expected this to use the vma->pages. I
think with the GGTT the vma will often create its own sg layout which !=
obj->mm.sgt. IIUC the async unbind will still call vma_unbind_pages
which might nuke the vma sgt? Or is something else going on here?
