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[PATCH v2 2/4] virtio-blk: Configure all host notifiers in a single MR t
From: |
Greg Kurz |
Subject: |
[PATCH v2 2/4] virtio-blk: Configure all host notifiers in a single MR transaction |
Date: |
Fri, 7 May 2021 18:59:03 +0200 |
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(+)
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index d7b5c95d26d9..55efded716e2 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -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);
}
--
2.26.3