Re: [PATCH 11/16] vhost: introduce restart and release for vhost_dev's vqs

[Kangjie Xu]

在 2022/7/26 12:13, Jason Wang 写道:
> 在 2022/7/18 19:17, Kangjie Xu 写道:
> > Introduce vhost_dev_virtqueue_restart(), which can restart the
> > virtqueue when the vhost has already started running.
> >
> > Meanwhile, vhost_dev_virtqueue_release(), which can ummap the
> > vrings and the desc of a specific vq of a device.
> >
> > Combining the two functions, we can reset a virtqueue with a
> > started vhost.
> >
> > Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >   hw/virtio/vhost.c         | 29 +++++++++++++++++++++++++++++
> >   include/hw/virtio/vhost.h |  6 ++++++
> >   2 files changed, 35 insertions(+)
> >
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > index e467dfc7bc..d158d71866 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -1904,3 +1904,32 @@ int vhost_net_set_backend(struct vhost_dev *hdev,
> >         return -ENOSYS;
> >   }
> > +
> > +void vhost_dev_virtqueue_release(struct vhost_dev *hdev, 
> > VirtIODevice *vdev,
> > +                                 int vq_index)
> > +{
> > +    int idx = vq_index - hdev->vq_index;
> > +
> > +    idx = hdev->vhost_ops->vhost_get_vq_index(hdev, idx);
> > +
> > +    vhost_virtqueue_unmap(hdev,
> > +                          vdev,
> > +                          hdev->vqs + idx,
> > +                          hdev->vq_index + idx);
> > +}
>
>
> Anything wrong that makes you can't use vhost_virtqueue_stop() here?
>
> Thanks
Yeah, vhost_virtqueue_stop() will result in all the queues in the device 
being stopped.

In the scenario of DPDK-OVS, vhost_virtqueue_stop will send 
VHOST_USER_GET_VRING_BASE to DPDK. This message is meant to destroy the 
queue.

However, In DPDK, VHOST_USER_GET_VRING_BASE message will lead to 
vhost_destroy_device_notify(). This function will disable all the queues 
in the device.

Thus, when restarting the queue, other queues except the restarted one 
are still disabled.

On the other hand, I think it may be not necessary to destroy the queue. 
We can simply disable it. When restarting the queue, it will be 
intialized again.

I'm sorry I forgot to cc in the last email, so I resend this email.

Thanks
> > +
> > +int vhost_dev_virtqueue_restart(struct vhost_dev *hdev, VirtIODevice 
> > *vdev,
> > +                                int vq_index)
> > +{
> > +    int idx = vq_index - hdev->vq_index;
> > +    int r = 0;
> > +
> > +    idx = hdev->vhost_ops->vhost_get_vq_index(hdev, idx);
> > +
> > +    r = vhost_virtqueue_start(hdev,
> > +                              vdev,
> > +                              hdev->vqs + idx,
> > +                              hdev->vq_index + idx);
> > +
> > +    return r;
> > +}
> > diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> > index a346f23d13..7df7dbe24d 100644
> > --- a/include/hw/virtio/vhost.h
> > +++ b/include/hw/virtio/vhost.h
> > @@ -277,6 +277,12 @@ bool vhost_has_free_slot(void);
> >   int vhost_net_set_backend(struct vhost_dev *hdev,
> >                             struct vhost_vring_file *file);
> >   +
> > +void vhost_dev_virtqueue_release(struct vhost_dev *hdev, 
> > VirtIODevice *vdev,
> > +                                 int vq_index);
> > +int vhost_dev_virtqueue_restart(struct vhost_dev *hdev, VirtIODevice 
> > *vdev,
> > +                                int vq_index);
> > +
> >   int vhost_device_iotlb_miss(struct vhost_dev *dev, uint64_t iova, 
> > int write);
> >     void vhost_dev_reset_inflight(struct vhost_inflight *inflight);