Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH v11 5/7] virtio_balloon: introduce migration primitives to balloon pages | Date | Mon, 12 Nov 2012 18:19:23 +1030 |
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Rafael Aquini <aquini@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.
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