From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40300) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XkDzY-0000cP-Kt for qemu-devel@nongnu.org; Fri, 31 Oct 2014 11:21:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xk11U-0000LK-Nc for qemu-devel@nongnu.org; Thu, 30 Oct 2014 21:29:10 -0400 Received: from szxga03-in.huawei.com ([119.145.14.66]:43997) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xk11U-0000KS-4B for qemu-devel@nongnu.org; Thu, 30 Oct 2014 21:29:04 -0400 From: Bin Wu Date: Fri, 31 Oct 2014 00:40:16 +0000 Message-ID: <1414716016-18004-1-git-send-email-wu.wubin@huawei.com> MIME-Version: 1.0 Content-Type: text/plain Subject: [Qemu-devel] [PATCH v2] hw/virtio/vring/event_idx: fix the vring_avail_event error List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: stefanha@gmail.com, pbonzini@redhat.com, famz@redhat.com, Bin Wu , mst@redhat.com The event idx in virtio is an effective way to reduce the number of interrupts and exits of the guest. When the guest puts an request into the virtio ring, it doesn't exit immediately to inform the backend. Instead, the guest checks the "avail" event idx to determine the notification. In virtqueue_pop, when a request is poped, the current avail event idx should be set to the number of vq->last_avail_idx. Signed-off-by: Bin Wu --- V2 -> V1: update the same code in hw/virtio/dataplane/vring.c (Stefan) --- hw/virtio/dataplane/vring.c | 8 ++++---- hw/virtio/virtio.c | 2 +- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/hw/virtio/dataplane/vring.c b/hw/virtio/dataplane/vring.c index 372706a..61f6d83 100644 --- a/hw/virtio/dataplane/vring.c +++ b/hw/virtio/dataplane/vring.c @@ -352,10 +352,6 @@ int vring_pop(VirtIODevice *vdev, Vring *vring, goto out; } - if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) { - vring_avail_event(&vring->vr) = vring->vr.avail->idx; - } - i = head; do { if (unlikely(i >= num)) { @@ -392,6 +388,10 @@ int vring_pop(VirtIODevice *vdev, Vring *vring, /* On success, increment avail index. */ vring->last_avail_idx++; + if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) { + vring_avail_event(&vring->vr) = vring->last_avail_idx; + } + return head; out: diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 2c236bf..013979a 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -469,7 +469,7 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem) i = head = virtqueue_get_head(vq, vq->last_avail_idx++); if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) { - vring_avail_event(vq, vring_avail_idx(vq)); + vring_avail_event(vq, vq->last_avail_idx); } if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_INDIRECT) { -- 1.7.12.4