[PATCH v1 1/3] virtio-pci: submit msi route changes in batch

[Longpeng(Mike)]

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.

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