[v3,2/2] virtio: improve virtio devices initialization time

The loading time of a VM is quite significant when its virtio
devices use a large amount of virt-queues (e.g. a virtio-serial
device with max_ports=511). Most of the time is spend in the
creation of all the required event notifiers (ioeventfd and memory
regions).

This patch pack all the changes to the memory regions in a
single memory transaction.

Reported-by: Sitong Liu <address@hidden>
Reported-by: Xiaoling Gao <address@hidden>
Signed-off-by: Gal Hammer <ghammer@redhat.com>
---
 hw/virtio/virtio.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

On Mon, Jan 29, 2018 at 04:20:57PM +0200, Gal Hammer wrote:
> The loading time of a VM is quite significant when its virtio
> devices use a large amount of virt-queues (e.g. a virtio-serial
> device with max_ports=511). Most of the time is spend in the
> creation of all the required event notifiers (ioeventfd and memory
> regions).
> 
> This patch pack all the changes to the memory regions in a
> single memory transaction.
> 
> Reported-by: Sitong Liu <address@hidden>
> Reported-by: Xiaoling Gao <address@hidden>

Just a small note: the way to hide the address is not to put it in:

Reported-by: Sitong Liu
Reported-by: Xiaoling Gao

a stub email isn't needed, it merely confuses tools.

I've fixed this up for now, no need to worry.

> Signed-off-by: Gal Hammer <ghammer@redhat.com>
> ---
>  hw/virtio/virtio.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 3667cd6..006d3d1 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -2572,8 +2572,9 @@ static Property virtio_properties[] = {
>  static int virtio_device_start_ioeventfd_impl(VirtIODevice *vdev)
>  {
>      VirtioBusState *qbus = VIRTIO_BUS(qdev_get_parent_bus(DEVICE(vdev)));
> -    int n, r, err;
> +    int i, n, r, err;
>  
> +    memory_region_transaction_begin();
>      for (n = 0; n < VIRTIO_QUEUE_MAX; n++) {
>          VirtQueue *vq = &vdev->vq[n];
>          if (!virtio_queue_get_num(vdev, n)) {
> @@ -2596,9 +2597,11 @@ static int virtio_device_start_ioeventfd_impl(VirtIODevice *vdev)
>          }
>          event_notifier_set(&vq->host_notifier);
>      }
> +    memory_region_transaction_commit();
>      return 0;
>  
>  assign_error:
> +    i = n; /* save n for a second iteration after transaction is committed. */
>      while (--n >= 0) {
>          VirtQueue *vq = &vdev->vq[n];
>          if (!virtio_queue_get_num(vdev, n)) {
> @@ -2608,7 +2611,14 @@ assign_error:
>          event_notifier_set_handler(&vq->host_notifier, NULL);
>          r = virtio_bus_set_host_notifier(qbus, n, false);
>          assert(r >= 0);
> -        virtio_bus_cleanup_host_notifier(qbus, n);
> +    }
> +    memory_region_transaction_commit();
> +
> +    while (--i >= 0) {
> +        if (!virtio_queue_get_num(vdev, i)) {
> +            continue;
> +        }
> +        virtio_bus_cleanup_host_notifier(qbus, i);
>      }
>      return err;
>  }
> @@ -2626,6 +2636,7 @@ static void virtio_device_stop_ioeventfd_impl(VirtIODevice *vdev)
>      VirtioBusState *qbus = VIRTIO_BUS(qdev_get_parent_bus(DEVICE(vdev)));
>      int n, r;
>  
> +    memory_region_transaction_begin();
>      for (n = 0; n < VIRTIO_QUEUE_MAX; n++) {
>          VirtQueue *vq = &vdev->vq[n];
>  
> @@ -2635,6 +2646,13 @@ static void virtio_device_stop_ioeventfd_impl(VirtIODevice *vdev)
>          event_notifier_set_handler(&vq->host_notifier, NULL);
>          r = virtio_bus_set_host_notifier(qbus, n, false);
>          assert(r >= 0);
> +    }
> +    memory_region_transaction_commit();
> +
> +    for (n = 0; n < VIRTIO_QUEUE_MAX; n++) {
> +        if (!virtio_queue_get_num(vdev, n)) {
> +            continue;
> +        }
>          virtio_bus_cleanup_host_notifier(qbus, n);
>      }
>  }
> -- 
> 2.7.5