Re: [PATCH v11 6/6] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ

On Fri, Jun 09, 2017 at 06:41:41PM +0800, Wei Wang wrote:

-	if (!virtqueue_indirect_desc_table_add(vq, desc, num)) {
+	if (!virtqueue_indirect_desc_table_add(vq, desc, *num)) {
 		virtqueue_kick(vq);
-		wait_event(vb->acked, virtqueue_get_buf(vq, &len));
-		vb->balloon_page_chunk.chunk_num = 0;
+		if (busy_wait)
+			while (!virtqueue_get_buf(vq, &len) &&
+			       !virtqueue_is_broken(vq))
+				cpu_relax();
+		else
+			wait_event(vb->acked, virtqueue_get_buf(vq, &len));

This is something I didn't previously notice.
As you always keep a single buffer in flight, you do not
really need indirect at all. Just add all descriptors
in the ring directly, then kick.

E.g.
	virtqueue_add_first
	virtqueue_add_next
	virtqueue_add_last

?

You also want a flag to avoid allocations but there's no need to do it
per descriptor, set it on vq.

-- 
MST