On Wed, 5 May 2021 11:14:23 +0100 Stefan Hajnoczi <stefa...@redhat.com> wrote:
> 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.
>
Indeed. Same goes for patch 4 actually.
Michael,
Should I re-post an updated version of this series or can the
comments be added in a followup ?
> > +
> > /* 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.
True. I can drop this if I repost.
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