On Tue, Feb 28, 2023 at 05:39:35PM +0800, Longpeng(Mike) wrote:
> From: Longpeng <longpe...@huawei.com>
>
> The kvm_irqchip_commit_routes() is a time-intensive operation, it needs
> scan and update all irqfds that are already assigned during each invocation,
> so more vectors means need more time to process them. For virtio-pci, we
> can just submit once when enabling vectors of a virtio-pci device.
>
> This can reduce the downtime when migrating a VM with vhost-vdpa devices.
can in what sense? does it or does it not? by how much?
> Signed-off-by: Longpeng <longpe...@huawei.com>
> ---
> hw/virtio/virtio-pci.c | 24 +++++++++++++++++++++---
> 1 file changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 247325c193..22e76e3902 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -49,6 +49,19 @@
> * configuration space */
> #define VIRTIO_PCI_CONFIG_SIZE(dev)
> VIRTIO_PCI_CONFIG_OFF(msix_enabled(dev))
>
> +/* Protected by the BQL */
> +static KVMRouteChange virtio_pci_route_change;
> +
> +static inline void virtio_pci_begin_route_changes(void)
> +{
> + virtio_pci_route_change = kvm_irqchip_begin_route_changes(kvm_state);
> +}
> +
> +static inline void virtio_pci_commit_route_changes(void)
> +{
> + kvm_irqchip_commit_route_changes(&virtio_pci_route_change);
> +}
> +
> static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size,
> VirtIOPCIProxy *dev);
> static void virtio_pci_reset(DeviceState *qdev);
> @@ -790,12 +803,11 @@ static int kvm_virtio_pci_vq_vector_use(VirtIOPCIProxy
> *proxy,
> int ret;
>
> if (irqfd->users == 0) {
> - KVMRouteChange c = kvm_irqchip_begin_route_changes(kvm_state);
> - ret = kvm_irqchip_add_msi_route(&c, vector, &proxy->pci_dev);
> + ret = kvm_irqchip_add_msi_route(&virtio_pci_route_change, vector,
> + &proxy->pci_dev);
> if (ret < 0) {
> return ret;
> }
> - kvm_irqchip_commit_route_changes(&c);
> irqfd->virq = ret;
> }
> irqfd->users++;
> @@ -903,12 +915,18 @@ static int kvm_virtio_pci_vector_vq_use(VirtIOPCIProxy
> *proxy, int nvqs)
> int ret = 0;
> VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
>
> + virtio_pci_begin_route_changes();
> +
> for (queue_no = 0; queue_no < nvqs; queue_no++) {
> if (!virtio_queue_get_num(vdev, queue_no)) {
> + virtio_pci_commit_route_changes();
> return -1;
> }
> ret = kvm_virtio_pci_vector_use_one(proxy, queue_no);
> }
> +
> + virtio_pci_commit_route_changes();
> +
> return ret;
> }
>
> --
> 2.23.0
