On Thu, 28 Jul 2022 10:38:51 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> On Wed, Jul 27, 2022 at 3:44 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> >
> > On Wed, 27 Jul 2022 11:12:19 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > >
> > > 在 2022/7/26 15:21, Xuan Zhuo 写道:
> > > > virtio ring split supports resize.
> > > >
> > > > Only after the new vring is successfully allocated based on the new num,
> > > > we will release the old vring. In any case, an error is returned,
> > > > indicating that the vring still points to the old vring.
> > > >
> > > > In the case of an error, re-initialize(virtqueue_reinit_split()) the
> > > > virtqueue to ensure that the vring can be used.
> > > >
> > > > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > > Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> > > > ---
> > > > drivers/virtio/virtio_ring.c | 34 ++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 34 insertions(+)
> > > >
> > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > index b6fda91c8059..58355e1ac7d7 100644
> > > > --- a/drivers/virtio/virtio_ring.c
> > > > +++ b/drivers/virtio/virtio_ring.c
> > > > @@ -220,6 +220,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index,
> > > > void (*callback)(struct virtqueue *),
> > > > const char *name);
> > > > static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num);
> > > > +static void vring_free(struct virtqueue *_vq);
> > > >
> > > > /*
> > > > * Helpers.
> > > > @@ -1117,6 +1118,39 @@ static struct virtqueue *vring_create_virtqueue_split(
> > > > return vq;
> > > > }
> > > >
> > > > +static int virtqueue_resize_split(struct virtqueue *_vq, u32 num)
> > > > +{
> > > > + struct vring_virtqueue_split vring_split = {};
> > > > + struct vring_virtqueue *vq = to_vvq(_vq);
> > > > + struct virtio_device *vdev = _vq->vdev;
> > > > + int err;
> > > > +
> > > > + err = vring_alloc_queue_split(&vring_split, vdev, num,
> > > > + vq->split.vring_align,
> > > > + vq->split.may_reduce_num);
> > > > + if (err)
> > > > + goto err;
> > >
> > >
> > > I think we don't need to do anything here?
> >
> > Am I missing something?
>
> I meant it looks to me most of the virtqueue_reinit() is unnecessary.
> We probably only need to reinit avail/used idx there.
In this function, we can indeed remove some code.
> static void virtqueue_reinit_split(struct vring_virtqueue *vq)
> {
> int size, i;
>
> memset(vq->split.vring.desc, 0, vq->split.queue_size_in_bytes);
>
> size = sizeof(struct vring_desc_state_split) * vq->split.vring.num;
> memset(vq->split.desc_state, 0, size);
>
> size = sizeof(struct vring_desc_extra) * vq->split.vring.num;
> memset(vq->split.desc_extra, 0, size);
These memsets can be removed, and theoretically it will not cause any
exceptions.
>
>
>
> for (i = 0; i < vq->split.vring.num - 1; i++)
> vq->split.desc_extra[i].next = i + 1;
This can also be removed, but we need to record free_head that will been update
inside virtqueue_init().
>
> virtqueue_init(vq, vq->split.vring.num);
There are some operations in this, which can also be skipped, such as setting
use_dma_api. But I think calling this function directly will be more convenient
for maintenance.
> virtqueue_vring_init_split(&vq->split, vq);
virtqueue_vring_init_split() is necessary.
> }
Another method, we can take out all the variables to be reinitialized
separately, and repackage them into a new function. I don’t think it’s worth
it, because this path will only be reached if the memory allocation fails, which
is a rare occurrence. In this case, doing so will increase the cost of
maintenance. If you think so also, I will remove the above memset in the next
version.
Thanks.
>
> Thanks
>
> >
> > >
> > >
> > > > +
> > > > + err = vring_alloc_state_extra_split(&vring_split);
> > > > + if (err) {
> > > > + vring_free_split(&vring_split, vdev);
> > > > + goto err;
> > >
> > >
> > > I suggest to move vring_free_split() into a dedicated error label.
> >
> > Will change.
> >
> > Thanks.
> >
> >
> > >
> > > Thanks
> > >
> > >
> > > > + }
> > > > +
> > > > + vring_free(&vq->vq);
> > > > +
> > > > + virtqueue_vring_init_split(&vring_split, vq);
> > > > +
> > > > + virtqueue_init(vq, vring_split.vring.num);
> > > > + virtqueue_vring_attach_split(vq, &vring_split);
> > > > +
> > > > + return 0;
> > > > +
> > > > +err:
> > > > + virtqueue_reinit_split(vq);
> > > > + return -ENOMEM;
> > > > +}
> > > > +
> > > >
> > > > /*
> > > > * Packed ring specific functions - *_packed().
> > >
> >
>
