[Qemu-devel] [PATCH 1/9] virtio-blk: use batch notify in non-dataplane case

[Stefan Hajnoczi <stefanha@redhat.com>]

Commit 5b2ffbe4d99843fd8305c573a100047a8c962327 ("virtio-blk: dataplane:
notify guest as a batch") deferred guest notification to a BH in order
batch notifications.  This optimization is not specific to dataplane so
move it to the generic virtio-blk code that is shared by both dataplane
and non-dataplane code.

Note that this patch adds a flush function to force pending
notifications.  This way we can ensure notifications do not cross device
reset or vmstate saving.

Cc: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 10 ----------
 hw/block/virtio-blk.c           | 37 +++++++++++++++++++++++++++++++------
 include/hw/virtio/virtio-blk.h  |  1 +
 3 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 3cb97c9..e0ac4f4 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -35,7 +35,6 @@ struct VirtIOBlockDataPlane {
     VirtIODevice *vdev;
     VirtQueue *vq;                  /* virtqueue vring */
     EventNotifier *guest_notifier;  /* irq */
-    QEMUBH *bh;                     /* bh for guest notification */
 
     Notifier insert_notifier, remove_notifier;
 
@@ -54,13 +53,6 @@ struct VirtIOBlockDataPlane {
 /* Raise an interrupt to signal guest, if necessary */
 void virtio_blk_data_plane_notify(VirtIOBlockDataPlane *s)
 {
-    qemu_bh_schedule(s->bh);
-}
-
-static void notify_guest_bh(void *opaque)
-{
-    VirtIOBlockDataPlane *s = opaque;
-
     if (!virtio_should_notify(s->vdev, s->vq)) {
         return;
     }
@@ -156,7 +148,6 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
         object_ref(OBJECT(s->iothread));
     }
     s->ctx = iothread_get_aio_context(s->iothread);
-    s->bh = aio_bh_new(s->ctx, notify_guest_bh, s);
 
     s->insert_notifier.notify = data_plane_blk_insert_notifier;
     s->remove_notifier.notify = data_plane_blk_remove_notifier;
@@ -179,7 +170,6 @@ void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
     data_plane_remove_op_blockers(s);
     notifier_remove(&s->insert_notifier);
     notifier_remove(&s->remove_notifier);
-    qemu_bh_delete(s->bh);
     object_unref(OBJECT(s->iothread));
     g_free(s);
 }
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 284e646..0eaf6bf 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -45,20 +45,37 @@ void virtio_blk_free_request(VirtIOBlockReq *req)
     }
 }
 
+/* Many requests can complete in an event loop iteration, we only notify the
+ * guest once.
+ */
+static void virtio_blk_batch_notify_bh(void *opaque)
+{
+    VirtIOBlock *s = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    if (s->dataplane_started && !s->dataplane_disabled) {
+        virtio_blk_data_plane_notify(s->dataplane);
+    } else {
+        virtio_notify(vdev, s->vq);
+    }
+}
+
+/* Force batch notifications to run */
+static void virtio_blk_batch_notify_flush(VirtIOBlock *s)
+{
+    qemu_bh_cancel(s->batch_notify_bh);
+    virtio_blk_batch_notify_bh(s);
+}
+
 static void virtio_blk_req_complete(VirtIOBlockReq *req, unsigned char status)
 {
     VirtIOBlock *s = req->dev;
-    VirtIODevice *vdev = VIRTIO_DEVICE(s);
 
     trace_virtio_blk_req_complete(req, status);
 
     stb_p(&req->in->status, status);
     virtqueue_push(s->vq, &req->elem, req->in_len);
-    if (s->dataplane_started && !s->dataplane_disabled) {
-        virtio_blk_data_plane_notify(s->dataplane);
-    } else {
-        virtio_notify(vdev, s->vq);
-    }
+    qemu_bh_schedule(s->batch_notify_bh);
 }
 
 static int virtio_blk_handle_rw_error(VirtIOBlockReq *req, int error,
@@ -664,6 +681,8 @@ static void virtio_blk_reset(VirtIODevice *vdev)
     if (s->dataplane) {
         virtio_blk_data_plane_stop(s->dataplane);
     }
+
+    virtio_blk_batch_notify_flush(s);
     aio_context_release(ctx);
 
     blk_set_enable_write_cache(s->blk, s->original_wce);
@@ -801,6 +820,8 @@ static void virtio_blk_save(QEMUFile *f, void *opaque)
         virtio_blk_data_plane_stop(s->dataplane);
     }
 
+    virtio_blk_batch_notify_flush(s);
+
     virtio_save(vdev, f);
 }
     
@@ -896,6 +917,9 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
+    s->batch_notify_bh = aio_bh_new(blk_get_aio_context(s->blk),
+                                    virtio_blk_batch_notify_bh, s);
+
     s->change = qemu_add_vm_change_state_handler(virtio_blk_dma_restart_cb, s);
     register_savevm(dev, "virtio-blk", virtio_blk_id++, 2,
                     virtio_blk_save, virtio_blk_load, s);
@@ -910,6 +934,7 @@ static void virtio_blk_device_unrealize(DeviceState *dev, Error **errp)
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VirtIOBlock *s = VIRTIO_BLK(dev);
 
+    qemu_bh_delete(s->batch_notify_bh);
     virtio_blk_data_plane_destroy(s->dataplane);
     s->dataplane = NULL;
     qemu_del_vm_change_state_handler(s->change);
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 8f2b056..b3834bc 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -49,6 +49,7 @@ typedef struct VirtIOBlock {
     VirtQueue *vq;
     void *rq;
     QEMUBH *bh;
+    QEMUBH *batch_notify_bh;
     VirtIOBlkConf conf;
     unsigned short sector_mask;
     bool original_wce;
-- 
2.5.5