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[PATCH v2 4/4] virtio-scsi: Configure all host notifiers in a single MR
From: |
Greg Kurz |
Subject: |
[PATCH v2 4/4] virtio-scsi: Configure all host notifiers in a single MR transaction |
Date: |
Fri, 7 May 2021 18:59:05 +0200 |
This allows the virtio-scsi-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 6m5.563s down to 1m2.884s 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>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
hw/scsi/virtio-scsi-dataplane.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index b2cb3d9dcc64..18eb824c97f5 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -152,6 +152,12 @@ int virtio_scsi_dataplane_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();
+
rc = virtio_scsi_set_host_notifier(s, vs->ctrl_vq, 0);
if (rc != 0) {
goto fail_host_notifiers;
@@ -173,6 +179,8 @@ int virtio_scsi_dataplane_start(VirtIODevice *vdev)
vq_init_count++;
}
+ memory_region_transaction_commit();
+
aio_context_acquire(s->ctx);
virtio_queue_aio_set_host_notifier_handler(vs->ctrl_vq, s->ctx,
virtio_scsi_data_plane_handle_ctrl);
@@ -192,6 +200,15 @@ int virtio_scsi_dataplane_start(VirtIODevice *vdev)
fail_host_notifiers:
for (i = 0; i < vq_init_count; 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 < vq_init_count; i++) {
virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
}
k->set_guest_notifiers(qbus->parent, vs->conf.num_queues + 2, false);
@@ -229,8 +246,23 @@ void virtio_scsi_dataplane_stop(VirtIODevice *vdev)
blk_drain_all(); /* ensure there are no in-flight requests */
+ /*
+ * 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 < vs->conf.num_queues + 2; 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 < vs->conf.num_queues + 2; i++) {
virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
}
--
2.26.3