commit 89d62be9f4fb538db7f919a2be7df2544ffc02c5
author Michael S. Tsirkin <mst@redhat.com> Tue Dec 18 14:02:46 2012 +0200
committer Michael S. Tsirkin <mst@redhat.com> Wed Dec 26 11:49:29 2012 +0200
tree 5a19bad2746869cf396e85f55c196bddf660244b
parent 70f8ee395afda6d96b15cb9a5b311af7720dded0

virtio-pci: don't poll masked vectors

At the moment, when irqfd is in use but a vector is masked,
qemu will poll it and handle vector masks in userspace.
Since almost no one ever looks at the pending bits,
it is better to defer this until pending bits
are actually read.
Implement this optimization using the new poll notifier.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio-pci.c

diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 37e8b2d..af9a56c 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -508,8 +508,6 @@
         }
         return ret;
     }
-
-    virtio_queue_set_guest_notifier_fd_handler(vq, true, true);
     return 0;
 }
 
@@ -528,8 +526,6 @@
     if (--irqfd->users == 0) {
         kvm_irqchip_release_virq(kvm_state, irqfd->virq);
     }
-
-    virtio_queue_set_guest_notifier_fd_handler(vq, true, false);
 }
 
 static int kvm_virtio_pci_vector_use(PCIDevice *dev, unsigned vector,
@@ -580,7 +576,36 @@
     }
 }
 
-static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign)
+static void kvm_virtio_pci_vector_poll(PCIDevice *dev,
+                                       unsigned int vector_start,
+                                       unsigned int vector_end)
+{
+    VirtIOPCIProxy *proxy = container_of(dev, VirtIOPCIProxy, pci_dev);
+    VirtIODevice *vdev = proxy->vdev;
+    int queue_no;
+    unsigned int vector;
+    EventNotifier *notifier;
+    VirtQueue *vq;
+
+    for (queue_no = 0; queue_no < VIRTIO_PCI_QUEUE_MAX; queue_no++) {
+        if (!virtio_queue_get_num(vdev, queue_no)) {
+            break;
+        }
+        vector = virtio_queue_vector(vdev, queue_no);
+        if (vector < vector_start || vector >= vector_end ||
+            !msix_is_masked(dev, vector)) {
+            continue;
+        }
+        vq = virtio_get_queue(vdev, queue_no);
+        notifier = virtio_queue_get_guest_notifier(vq);
+        if (event_notifier_test_and_clear(notifier)) {
+            msix_set_pending(dev, vector);
+        }
+    }
+}
+
+static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign,
+                                         bool with_irqfd)
 {
     VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
     VirtQueue *vq = virtio_get_queue(proxy->vdev, n);
@@ -591,9 +616,9 @@
         if (r < 0) {
             return r;
         }
-        virtio_queue_set_guest_notifier_fd_handler(vq, true, false);
+        virtio_queue_set_guest_notifier_fd_handler(vq, true, with_irqfd);
     } else {
-        virtio_queue_set_guest_notifier_fd_handler(vq, false, false);
+        virtio_queue_set_guest_notifier_fd_handler(vq, false, with_irqfd);
         event_notifier_cleanup(notifier);
     }
 
@@ -611,9 +636,11 @@
     VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
     VirtIODevice *vdev = proxy->vdev;
     int r, n;
+    bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
+        kvm_msi_via_irqfd_enabled();
 
     /* Must unset vector notifier while guest notifier is still assigned */
-    if (kvm_msi_via_irqfd_enabled() && !assign) {
+    if (proxy->vector_irqfd && !assign) {
         msix_unset_vector_notifiers(&proxy->pci_dev);
         g_free(proxy->vector_irqfd);
         proxy->vector_irqfd = NULL;
@@ -624,21 +651,22 @@
             break;
         }
 
-        r = virtio_pci_set_guest_notifier(d, n, assign);
+        r = virtio_pci_set_guest_notifier(d, n, assign,
+                                          kvm_msi_via_irqfd_enabled());
         if (r < 0) {
             goto assign_error;
         }
     }
 
     /* Must set vector notifier after guest notifier has been assigned */
-    if (kvm_msi_via_irqfd_enabled() && assign) {
+    if (with_irqfd && assign) {
         proxy->vector_irqfd =
             g_malloc0(sizeof(*proxy->vector_irqfd) *
                       msix_nr_vectors_allocated(&proxy->pci_dev));
         r = msix_set_vector_notifiers(&proxy->pci_dev,
                                       kvm_virtio_pci_vector_use,
                                       kvm_virtio_pci_vector_release,
-                                      NULL);
+                                      kvm_virtio_pci_vector_poll);
         if (r < 0) {
             goto assign_error;
         }
@@ -650,7 +678,7 @@
     /* We get here on assignment failure. Recover by undoing for VQs 0 .. n. */
     assert(assign);
     while (--n >= 0) {
-        virtio_pci_set_guest_notifier(d, n, !assign);
+        virtio_pci_set_guest_notifier(d, n, !assign, with_irqfd);
     }
     return r;
 }