[Qemu-devel] [PATCH v3 2/7] virtio-blk: multiqueue batch notify

[Stefan Hajnoczi]

The batch notification BH needs to know which virtqueues to notify when
multiqueue is enabled.  Use a bitmap to track the virtqueues with
pending notifications.

At this point there is only one virtqueue so hard-code virtqueue index
0.  A later patch will switch to real virtqueue indices.

Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 3cb97c9..4439c7b 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -34,8 +34,8 @@ struct VirtIOBlockDataPlane {
 
     VirtIODevice *vdev;
     VirtQueue *vq;                  /* virtqueue vring */
-    EventNotifier *guest_notifier;  /* irq */
     QEMUBH *bh;                     /* bh for guest notification */
+    unsigned long *batch_notify_vqs;
 
     Notifier insert_notifier, remove_notifier;
 
@@ -54,18 +54,34 @@ struct VirtIOBlockDataPlane {
 /* Raise an interrupt to signal guest, if necessary */
 void virtio_blk_data_plane_notify(VirtIOBlockDataPlane *s)
 {
+    set_bit(0, s->batch_notify_vqs);
     qemu_bh_schedule(s->bh);
 }
 
 static void notify_guest_bh(void *opaque)
 {
     VirtIOBlockDataPlane *s = opaque;
+    unsigned nvqs = s->conf->num_queues;
+    unsigned long bitmap[BITS_TO_LONGS(nvqs)];
+    unsigned j;
 
-    if (!virtio_should_notify(s->vdev, s->vq)) {
-        return;
+    memcpy(bitmap, s->batch_notify_vqs, sizeof(bitmap));
+    memset(s->batch_notify_vqs, 0, sizeof(bitmap));
+
+    for (j = 0; j < nvqs; j += BITS_PER_LONG) {
+        unsigned long bits = bitmap[j];
+
+        while (bits != 0) {
+            unsigned i = j + ctzl(bits);
+            VirtQueue *vq = virtio_get_queue(s->vdev, i);
+
+            if (virtio_should_notify(s->vdev, vq)) {
+                event_notifier_set(virtio_queue_get_guest_notifier(vq));
+            }
+
+            bits &= bits - 1; /* clear right-most bit */
+        }
     }
-
-    event_notifier_set(s->guest_notifier);
 }
 
 static void data_plane_set_up_op_blockers(VirtIOBlockDataPlane *s)
@@ -157,6 +173,7 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, 
VirtIOBlkConf *conf,
     }
     s->ctx = iothread_get_aio_context(s->iothread);
     s->bh = aio_bh_new(s->ctx, notify_guest_bh, s);
+    s->batch_notify_vqs = bitmap_new(conf->num_queues);
 
     s->insert_notifier.notify = data_plane_blk_insert_notifier;
     s->remove_notifier.notify = data_plane_blk_remove_notifier;
@@ -179,6 +196,7 @@ void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
     data_plane_remove_op_blockers(s);
     notifier_remove(&s->insert_notifier);
     notifier_remove(&s->remove_notifier);
+    g_free(s->batch_notify_vqs);
     qemu_bh_delete(s->bh);
     object_unref(OBJECT(s->iothread));
     g_free(s);
@@ -217,7 +235,6 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
                 "ensure -enable-kvm is set\n", r);
         goto fail_guest_notifiers;
     }
-    s->guest_notifier = virtio_queue_get_guest_notifier(s->vq);
 
     /* Set up virtqueue notify */
     r = k->set_host_notifier(qbus->parent, 0, true);
-- 
2.5.5