@@ -198,19 +198,38 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
goto fail_guest_notifiers;
}
+ /*
+ * Batch all the host notifiers in a single transaction to avoid
+ * quadratic time complexity in address_space_update_ioeventfds().
+ */
+ memory_region_transaction_begin();
+
/* 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);
+ }
+
+ /*
+ * The transaction expects the ioeventfds to be open when it
+ * commits. Do it now, before the cleanup loop.
+ */
+ 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);
@@ -312,8 +331,23 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
aio_context_release(s->ctx);
+ /*
+ * Batch all the host notifiers in a single transaction to avoid
+ * quadratic time complexity in address_space_update_ioeventfds().
+ */
+ memory_region_transaction_begin();
+
for (i = 0; i < nvqs; i++) {
virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
+ }
+
+ /*
+ * The transaction expects the ioeventfds to be open when it
+ * commits. Do it now, before the cleanup loop.
+ */
+ memory_region_transaction_commit();
+
+ for (i = 0; i < nvqs; i++) {
virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
}
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 <groug@kaod.org> --- hw/block/dataplane/virtio-blk.c | 34 +++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+)