From: Longpeng <longpe...@huawei.com> This allows the vhost device to batch the setup of all its host notifiers. This significantly reduces the device starting time, e.g. the vhost-vDPA generic device [1] start time reduce from 376ms to 9.1ms for a VM with 64 vCPUs and 3 vDPA device(64vq per device).
[1] https://www.mail-archive.com/qemu-devel@nongnu.org/msg921541.html Signed-off-by: Longpeng <longpe...@huawei.com> --- hw/virtio/vhost.c | 39 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 38 insertions(+), 1 deletion(-) diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index d1c4c20b8c..bf82d9b176 100644 --- a/hw/virtio/vhost.c +++ b/hw/virtio/vhost.c @@ -1507,6 +1507,7 @@ void vhost_dev_cleanup(struct vhost_dev *hdev) int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev) { BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev))); + int vq_init_count = 0; int i, r, e; /* We will pass the notifiers to the kernel, make sure that QEMU @@ -1518,6 +1519,12 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev) goto fail; } + /* + * 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 < hdev->nvqs; ++i) { r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i, true); @@ -1525,19 +1532,33 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev) error_report("vhost VQ %d notifier binding failed: %d", i, -r); goto fail_vq; } + + vq_init_count++; } + memory_region_transaction_commit(); + return 0; fail_vq: - while (--i >= 0) { + for (i = 0; i < vq_init_count; i++) { e = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i, false); if (e < 0) { error_report("vhost VQ %d notifier cleanup error: %d", i, -r); } assert (e >= 0); + } + + /* + * 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), hdev->vq_index + i); } + virtio_device_release_ioeventfd(vdev); fail: return r; @@ -1553,6 +1574,12 @@ void vhost_dev_disable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev) BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev))); int i, r; + /* + * 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 < hdev->nvqs; ++i) { r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i, false); @@ -1560,8 +1587,18 @@ void vhost_dev_disable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev) error_report("vhost VQ %d notifier cleanup failed: %d", i, -r); } assert (r >= 0); + } + + /* + * 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 < hdev->nvqs; ++i) { virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i); } + virtio_device_release_ioeventfd(vdev); } -- 2.23.0
