Rafael Aquini <aqu...@redhat.com> writes: > On Thu, Nov 08, 2012 at 09:32:18AM +1030, Rusty Russell wrote: >> The first one can be delayed, the second one can be delayed if the host >> didn't ask for VIRTIO_BALLOON_F_MUST_TELL_HOST (qemu doesn't). >> >> We could implement a proper request queue for these, and return -EAGAIN >> if the queue fills. Though in practice, it's not important (it might >> help performance). > > I liked the idea. Give me the directions to accomplish it and I'll give it a > try > for sure.
OK, let's get this applied first, but here are some pointers: Here's the current callback function when the host has processed the buffers we put in the queue: static void balloon_ack(struct virtqueue *vq) { struct virtio_balloon *vb = vq->vdev->priv; wake_up(&vb->acked); } It's almost a noop: here's how we use it to make our queues synchronous: static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) { struct scatterlist sg; unsigned int len; sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns); /* We should always be able to add one buffer to an empty queue. */ if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0) BUG(); virtqueue_kick(vq); /* When host has read buffer, this completes via balloon_ack */ wait_event(vb->acked, virtqueue_get_buf(vq, &len)); } And we set up the callback when we create the virtqueue: vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request }; ... err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names); So off the top of my head it should be as simple as changing tell_host() to only wait if the virtqueue_add_buf() fails (ie. queue is full). Hmm, though you will want to synchronize the inflate and deflate queues: if we tell the host we're giving a page up we want it to have seen that before we tell it we're using it again... Cheers, Rusty. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization