netdev - Re: [PATCH v13 16/42] virtio_ring: split: introduce virtqueue_resize

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Date:   Thu, 28 Jul 2022 10:38:51 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Vadim Pasternak <vadimp@...dia.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Eric Farman <farman@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-um@...ts.infradead.org, netdev <netdev@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm <kvm@...r.kernel.org>,
        "open list:XDP (eXpress Data Path)" <bpf@...r.kernel.org>,
        Kangjie Xu <kangjie.xu@...ux.alibaba.com>,
        virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v13 16/42] virtio_ring: split: introduce virtqueue_resize_split()

On Wed, Jul 27, 2022 at 3:44 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Wed, 27 Jul 2022 11:12:19 +0800, Jason Wang <jasowang@...hat.com> 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@...ux.alibaba.com>
> > > Acked-by: Jason Wang <jasowang@...hat.com>
> > > ---
> > >   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.

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().
> >
>