From bad54220ef2133fac3f1978f40d0e82f5b5dfc6c Mon Sep 17 00:00:00 2001
From: Vadim Rozenfeld <vrozenfe@redhat.com>
Date: Sun, 3 Jan 2010 21:55:56 -0200
Subject: [PATCH 4/6] Queue notify support for virtio block device.

RH-Author: Vadim Rozenfeld <vrozenfe@redhat.com>
Message-id: <4B41126C.9080906@redhat.com>
Patchwork-id: 6043
O-Subject: [RFC][PATCH] Queue notify support for virtio block device.
Bugzilla: 552250
RH-Acked-by: Dor Laor <dlaor@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
RH-Acked-by: Juan Quintela <quintela@redhat.com>

The following patch allows to reduce CPU utilization for Windows guests
running with virtio block devices.

repository: /home/vadimr/work/rhel5/kvm-userspace-rhel5
branch: rhel5/master
commit d1da74713a8d6a25ed8cdf212379f0aebe231135
Author: Vadim Rozenfeld <vadimr@localhost.localdomain>
Date:   Sun Jan 3 17:57:54 2010 +0200

    [RFC][PATCH] Queue notify support for virtio block device.

    Signed-off-by: Vadim Rozenfeld <vrozenfe@redhat.com>

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu/hw/virtio-blk.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/qemu/hw/virtio-blk.c b/qemu/hw/virtio-blk.c
index 6f74c25..720243d 100644
--- a/qemu/hw/virtio-blk.c
+++ b/qemu/hw/virtio-blk.c
@@ -24,6 +24,7 @@ typedef struct VirtIOBlock
     VirtQueue *vq;
     void *rq;
     QEMUBH *bh;
+    unsigned int pending;
 } VirtIOBlock;
 
 static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)
@@ -42,6 +43,7 @@ typedef struct VirtIOBlockReq
     struct VirtIOBlockReq *next;
 } VirtIOBlockReq;
 
+static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq);
 static void virtio_blk_req_complete(VirtIOBlockReq *req, int status)
 {
     VirtIOBlock *s = req->dev;
@@ -50,6 +52,10 @@ static void virtio_blk_req_complete(VirtIOBlockReq *req, int status)
     virtqueue_push(s->vq, &req->elem, req->size + sizeof(*req->in));
     virtio_notify(&s->vdev, s->vq);
 
+    virtio_blk_handle_output(&s->vdev, s->vq);
+    if(--s->pending == 0) 
+        virtio_queue_set_notification(s->vq, 1);
+
     qemu_free(req->buffer);
     qemu_free(req);
 }
@@ -200,6 +206,9 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
             exit(1);
         }
 
+        if(++s->pending == 1)
+            virtio_queue_set_notification(s->vq, 0);
+
         req->out = (void *)req->elem.out_sg[0].iov_base;
         req->in = (void *)req->elem.in_sg[req->elem.in_num - 1].iov_base;
 
-- 
1.6.3.rc4.29.g8146