From 0fdc6b8509f3d7663c2b5de164a5ab90173e2f19 Mon Sep 17 00:00:00 2001 From: Longpeng Date: Tue, 27 Dec 2022 15:20:14 +0800 Subject: [PATCH] vhost: configure all host notifiers in a single MR transaction MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This allows the vhost device to batch the setup of all its host notifiers. This significantly reduces the device starting time, e.g. the time spend on enabling notifiers reduce from 376ms to 9.1ms for a VM with 64 vCPUs and 3 vhost-vDPA generic devices (vdpa_sim_blk, 64vq per device) Signed-off-by: Longpeng Message-Id: <20221227072015.3134-3-longpeng2@huawei.com> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin Reviewed-by: Philippe Mathieu-Daudé --- hw/virtio/vhost.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index 87c49fa679..eb8c4c378c 100644 --- a/hw/virtio/vhost.c +++ b/hw/virtio/vhost.c @@ -1562,16 +1562,25 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev) return 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, true); if (r < 0) { error_report("vhost VQ %d notifier binding failed: %d", i, -r); + memory_region_transaction_commit(); vhost_dev_disable_notifiers(hdev, vdev); return r; } } + memory_region_transaction_commit(); + return 0; } @@ -1585,6 +1594,12 @@ 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); @@ -1592,6 +1607,15 @@ 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); -- 2.39.5