On Thu, Jan 11, 2018 at 9:52 PM, Michael S. Tsirkin <m...@redhat.com> wrote:
> On Thu, Jan 11, 2018 at 12:16:56PM +0200, Gal Hammer wrote: > > The loading time of a VM is quite significant when its virtio > > devices uses 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 <si...@redhat.com> > > Reported-by: Xiaoling Gao <xia...@redhat.com> > > Signed-off-by: Gal Hammer <gham...@redhat.com> > > Nice patch! Any timing numbers to share before/after? > Thanks. Unfortunately I made a mistake in the shutdown code (the transaction is wrapping the code which doesn't modify the memory regions), so a V2 is on its way. As for the timing. Running a VM with 25 virtio-serial devices, each one with max_ports=511, results in a boot time of around 30 minutes. With this patch (and a another patch to kvm) reduce it to approximately 3 minutes. This was reported and tracked here: https://bugzilla.redhat.com/show_bug.cgi?id=1528588 Gal. > > > --- > > hw/virtio/virtio.c | 11 +++++++++++ > > 1 file changed, 11 insertions(+) > > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > index ad564b0..8d8d93d 100644 > > --- a/hw/virtio/virtio.c > > +++ b/hw/virtio/virtio.c > > @@ -2574,6 +2574,7 @@ static int > > virtio_device_start_ioeventfd_impl(VirtIODevice > *vdev) > > VirtioBusState *qbus = VIRTIO_BUS(qdev_get_parent_ > bus(DEVICE(vdev))); > > int 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)) { > > @@ -2596,6 +2597,7 @@ static int > > virtio_device_start_ioeventfd_impl(VirtIODevice > *vdev) > > } > > event_notifier_set(&vq->host_notifier); > > } > > + memory_region_transaction_commit(); > > return 0; > > > > assign_error: > > @@ -2609,6 +2611,7 @@ assign_error: > > r = virtio_bus_set_host_notifier(qbus, n, false); > > assert(r >= 0); > > } > > + memory_region_transaction_commit(); > > return err; > > } > > > > @@ -2625,6 +2628,7 @@ 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]; > > > > @@ -2632,6 +2636,13 @@ static void > > virtio_device_stop_ioeventfd_impl(VirtIODevice > *vdev) > > continue; > > } > > event_notifier_set_handler(&vq->host_notifier, NULL); > > + } > > + memory_region_transaction_commit(); > > + > > + for (n = 0; n < VIRTIO_QUEUE_MAX; n++) { > > + if (!virtio_queue_get_num(vdev, n)) { > > + continue; > > + } > > r = virtio_bus_set_host_notifier(qbus, n, false); > > assert(r >= 0); > > } > > -- > > 2.7.5 >
