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

[Michael S. Tsirkin]

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