commit 0793169870f376bc9959b7d81df48ab4a90dcceb
author Fam Zheng <famz@redhat.com> Thu Feb 09 16:40:47 2017 +0800
committer Michael S. Tsirkin <mst@redhat.com> Fri Feb 17 21:52:30 2017 +0200
tree 706cd7d990534f97bcf1dd9ca8ca09c4e7d350ff
parent 4bb571d857d973d9308d9fdb1f48d983d6639bd4

virtio: Report real progress in VQ aio poll handler

In virtio_queue_host_notifier_aio_poll, not all "!virtio_queue_empty()"
cases are making true progress.

Currently the offending one is virtio-scsi event queue, whose handler
does nothing if no event is pending. As a result aio_poll() will spin on
the "non-empty" VQ and take 100% host CPU.

Fix this by reporting actual progress from virtio queue aio handlers.

Reported-by: Ed Swierk <eswierk@skyportsystems.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Tested-by: Ed Swierk <eswierk@skyportsystems.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio.c

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 6365706..2461c06 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -97,7 +97,7 @@
 
     uint16_t vector;
     VirtIOHandleOutput handle_output;
-    VirtIOHandleOutput handle_aio_output;
+    VirtIOHandleAIOOutput handle_aio_output;
     VirtIODevice *vdev;
     EventNotifier guest_notifier;
     EventNotifier host_notifier;
@@ -1287,14 +1287,16 @@
     virtio_queue_update_rings(vdev, n);
 }
 
-static void virtio_queue_notify_aio_vq(VirtQueue *vq)
+static bool virtio_queue_notify_aio_vq(VirtQueue *vq)
 {
     if (vq->vring.desc && vq->handle_aio_output) {
         VirtIODevice *vdev = vq->vdev;
 
         trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
-        vq->handle_aio_output(vdev, vq);
+        return vq->handle_aio_output(vdev, vq);
     }
+
+    return false;
 }
 
 static void virtio_queue_notify_vq(VirtQueue *vq)
@@ -2125,16 +2127,17 @@
 {
     EventNotifier *n = opaque;
     VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
+    bool progress;
 
     if (virtio_queue_empty(vq)) {
         return false;
     }
 
-    virtio_queue_notify_aio_vq(vq);
+    progress = virtio_queue_notify_aio_vq(vq);
 
     /* In case the handler function re-enabled notifications */
     virtio_queue_set_notification(vq, 0);
-    return true;
+    return progress;
 }
 
 static void virtio_queue_host_notifier_aio_poll_end(EventNotifier *n)
@@ -2146,7 +2149,7 @@
 }
 
 void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext *ctx,
-                                                VirtIOHandleOutput handle_output)
+                                                VirtIOHandleAIOOutput handle_output)
 {
     if (handle_output) {
         vq->handle_aio_output = handle_output;