[Qemu-devel] [PATCH 2/2] virtio-blk: dataplane: notify guest as a batch

[Ming Lei]

Now requests are submitted as a batch, so it is natural
to notify guest as a batch too.

This may supress interrupt  notification to VM:

        - in my test, decreased by ~13K/sec

Signed-off-by: Ming Lei <ming....@canonical.com>
---
 hw/block/dataplane/virtio-blk.c |   13 ++++++++++++-
 hw/block/virtio-blk.c           |    1 +
 include/hw/virtio/virtio-blk.h  |    1 +
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index e88862d..9d36659 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -45,6 +45,8 @@ struct VirtIOBlockDataPlane {
     AioContext *ctx;
     EventNotifier host_notifier;    /* doorbell */
 
+    VirtIOBlockReq *last_submit;
+
     /* Operation blocker on BDS */
     Error *blocker;
     void (*saved_complete_request)(struct VirtIOBlockReq *req,
@@ -67,7 +69,10 @@ static void complete_request_vring(VirtIOBlockReq *req, 
unsigned char status)
 
     vring_push(&req->dev->dataplane->vring, &req->elem,
                req->qiov.size + sizeof(*req->in));
-    notify_guest(req->dev->dataplane);
+
+    if (req->last) {
+        notify_guest(req->dev->dataplane);
+    }
 }
 
 static void handle_notify(EventNotifier *e)
@@ -101,6 +106,8 @@ static void handle_notify(EventNotifier *e)
                                                         req->elem.index);
 
             virtio_blk_handle_request(req, &mrb);
+
+            s->last_submit = req;
         }
 
         virtio_submit_multiwrite(s->blk->conf.bs, &mrb);
@@ -116,6 +123,10 @@ static void handle_notify(EventNotifier *e)
             break;
         }
     }
+
+    if (s->last_submit) {
+        s->last_submit->last = true;
+    }
     bdrv_io_unplug(s->blk->conf.bs);
 }
 
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 02cd6b0..86b37f7 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -35,6 +35,7 @@ VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
     req->dev = s;
     req->qiov.size = 0;
     req->next = NULL;
+    req->last = false;
     return req;
 }
 
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 992da26..07659c3 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -150,6 +150,7 @@ typedef struct VirtIOBlockReq {
     QEMUIOVector qiov;
     struct VirtIOBlockReq *next;
     BlockAcctCookie acct;
+    bool last;
 } VirtIOBlockReq;
 
 #define DEFINE_VIRTIO_BLK_FEATURES(_state, _field) \
-- 
1.7.9.5