On Mon, Nov 28, 2022 at 5:08 PM Longpeng (Mike, Cloud Infrastructure Service Product Dept.) <longpe...@huawei.com> wrote: > > > > 在 2022/11/21 12:01, Jason Wang 写道: > > On Fri, Nov 18, 2022 at 10:49 PM Longpeng(Mike) <longpe...@huawei.com> > > wrote: > >> > >> 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). > > > > Great, I think we need to do this for host_notifiers_mr as well. This > > helps for the case when the notification area could be mapped directly > > to guests. > > > Batch and commit once for host_notifiers_mrs can reduce the cost from > 423ms to 32ms, testing on vdpasim_blk (3 devices and 64 vqs per device) > with doorbell passthrough support. > I'll append a patch in the next version.
Great. Thanks > > >> > >> [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++; > >> } > > > > Nit, the name needs some tweak, it's actually the number of the host > > notifiers that is initialized. And we can count it out of the loop. > > > Ok, I will refer to virtio_device_start_ioeventfd_impl(). > > >> > >> + memory_region_transaction_commit(); > >> + > >> return 0; > >> fail_vq: > >> - while (--i >= 0) { > >> + for (i = 0; i < vq_init_count; i++) { > > > > It looks to me there's no need for this change. > > > > Others look good. > > > > Thanks > > > >> 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 > >> > > > > . >
