On Wed, Apr 07, 2021 at 04:34:59PM +0200, Greg Kurz wrote: > This allows the virtio-blk-pci device to batch the setup of all its > host notifiers. This significantly improves boot time of VMs with a > high number of vCPUs, e.g. from 3m26.186s down to 0m58.023s for a > pseries machine with 384 vCPUs. > > Note that memory_region_transaction_commit() must be called before > virtio_bus_cleanup_host_notifier() because the latter might close > ioeventfds that the transaction still assumes to be around when it > commits. > > Signed-off-by: Greg Kurz <gr...@kaod.org> > --- > hw/block/dataplane/virtio-blk.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c > index d7b5c95d26d9..cd81893d1d01 100644 > --- a/hw/block/dataplane/virtio-blk.c > +++ b/hw/block/dataplane/virtio-blk.c > @@ -198,19 +198,30 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev) > goto fail_guest_notifiers; > } > > + memory_region_transaction_begin();
This call is optional and an optimization. It would be nice to have a
comment here explaining that - otherwise people may wonder why this is
necessary.
> +
> /* Set up virtqueue notify */
> for (i = 0; i < nvqs; i++) {
> r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, true);
> if (r != 0) {
> + int j = i;
> +
> fprintf(stderr, "virtio-blk failed to set host notifier (%d)\n",
> r);
> while (i--) {
> virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
> + }
> +
> + memory_region_transaction_commit();
> +
> + while (j--) {
> virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
> }
> goto fail_host_notifiers;
> }
> }
>
> + memory_region_transaction_commit();
> +
> s->starting = false;
> vblk->dataplane_started = true;
> trace_virtio_blk_data_plane_start(s);
> @@ -246,8 +257,15 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
> return 0;
>
> fail_aio_context:
> + memory_region_transaction_begin();
Probably unnecessary since this is an error code path. We don't need to
optimize it.
Doesn't hurt though.
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