Re: [PATCH v1 6/7] vdpa: Add support for querying control virtqueue index

[Jason Wang <jasowang@redhat.com>]

On Thu, Dec 9, 2021 at 5:21 PM Eli Cohen <elic@nvidia.com> wrote:
>
> On Thu, Dec 09, 2021 at 05:12:01PM +0800, Jason Wang wrote:
> > On Thu, Dec 9, 2021 at 4:26 PM Eli Cohen <elic@nvidia.com> wrote:
> > >
> > > On Thu, Dec 09, 2021 at 04:17:22PM +0800, Jason Wang wrote:
> > > > On Thu, Dec 9, 2021 at 4:04 PM Eli Cohen <elic@nvidia.com> wrote:
> > > > >
> > > > > On Thu, Dec 09, 2021 at 03:55:48PM +0800, Jason Wang wrote:
> > > > > > On Thu, Dec 9, 2021 at 3:09 PM Eli Cohen <elic@nvidia.com> wrote:
> > > > > > >
> > > > > > > On Thu, Dec 09, 2021 at 01:44:56PM +0800, Jason Wang wrote:
> > > > > > > > On Thu, Dec 9, 2021 at 4:15 AM Eli Cohen <elic@nvidia.com> wrote:
> > > > > > > > >
> > > > > > > > > Add netlink attribute and callback function to query the control VQ
> > > > > > > > > index of a device.
> > > > > > > > >
> > > > > > > > > Example:
> > > > > > > > >
> > > > > > > > > $ vdpa dev config show vdpa-a
> > > > > > > > >   vdpa-a: mac 00:00:00:00:88:88 link up link_announce false max_vq_pairs 5 \
> > > > > > > > >   mtu 9000 ctrl_vq_idx 10
> > > > > > > >
> > > > > > > >
> > > > > > > > I still wonder about the motivation for this.
> > > > > > > To be able to show the stats for CVQ.
> > > > > >
> > > > > > Right.
> > > > > >
> > > > > > >
> > > > > > > > And as discussed, the
> > > > > > > > ctrl_vq_idx varies depending on whether MQ is negotiated.
> > > > > > >
> > > > > > > I handle this according to the spec and it depends on MQ.
> > > > > >
> > > > > > Yes, but there could be a chance that the cvq index changes after the
> > > > > > vdpa dev config show.
> > > > > >
> > > > >
> > > > > It depends on:
> > > > > VIRTIO_NET_F_CTRL_VQ
> > > > > VIRTIO_NET_F_MQ
> > > > >
> > > > > which can change only if the features are re-negotiated and that happens
> > > > > on driver in itialization.
> > > > >
> > > > > And on max_virtqueue_pairs which is also set at driver initialization.
> > > > >
> > > > > So I don't see any real issue here. Am I missing something?
> > > >
> > > > No. I meant technically there could be a re-negotiation that happens
> > > > in the middle:
> > > >
> > > > 1) vdpa dev config show
> > > > 2) feature renegotiation which change the cvq index
> > > > 3) getting cvq stats
> > > >
> > > > So the cvq index might be changed. E.g it could be changed from a cvq
> > > > to a rx queue. It might be easier to make the get index and stats
> > > > atomic.
> > > >
> > >
> > > The interface to read VQ stats is based on the user providing the index
> > > and getting the statistics.
> > >
> > > If we want to follow your suggestion then we need maybe to use a
> > > slightly modified command:
> > >
> > > For regular VQ:
> > > dpa dev vstats show vdpa-a qidx 0
> > >
> > > For CVQ:
> > > vdpa dev vstats show vdpa-a cvq
> >
> > This might be better, but we need to make sure cvq only works for the
> > device that has a cvq.
> >
>
> OK.
>
> > >
> > > And that raises another question. Do we want to report the CVQ index in
> > > config show?
> >
> > If we go with stats show vdpa-a cvq, we don't need to report the cvq index.
> >
>
> Maybe we should leave some kind of indication as to whether there is a
> CVQ. Maybe not the index itself by just "CVQ" so a user will know if
> it's worth trying to read cvq stats.
>
> Otherwise, the user will attempt to read and fail.
> What do you think?

I agree.

Thanks

>
> > Thanks
> >
> > >
> > > > Thanks
> > > >
> > > > >
> > > > > > Thanks
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > Thanks
> > > > > > > >
> > > > > > > > >
> > > > > > > > > Signed-off-by: Eli Cohen <elic@nvidia.com>
> > > > > > > > > ---
> > > > > > > > > v0 -> v1:
> > > > > > > > > 1. Use logic defined in the spec to deduce virtqueue index.
> > > > > > > > >
> > > > > > > > >  drivers/vdpa/vdpa.c       | 25 +++++++++++++++++++++++++
> > > > > > > > >  include/uapi/linux/vdpa.h |  1 +
> > > > > > > > >  2 files changed, 26 insertions(+)
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> > > > > > > > > index 3bf016e03512..b4d4b8a7ca4e 100644
> > > > > > > > > --- a/drivers/vdpa/vdpa.c
> > > > > > > > > +++ b/drivers/vdpa/vdpa.c
> > > > > > > > > @@ -712,6 +712,27 @@ static int vdpa_nl_cmd_dev_get_dumpit(struct sk_buff *msg, struct netlink_callba
> > > > > > > > >         return msg->len;
> > > > > > > > >  }
> > > > > > > > >
> > > > > > > > > +static int vdpa_dev_net_ctrl_vq_fill(struct vdpa_device *vdev,
> > > > > > > > > +                                    struct sk_buff *msg,
> > > > > > > > > +                                    struct virtio_net_config *config,
> > > > > > > > > +                                    u64 features)
> > > > > > > > > +{
> > > > > > > > > +       u16 N;
> > > > > > > > > +
> > > > > > > > > +       /* control VQ index, if available, is deduced according to the logic
> > > > > > > > > +        * described in the virtio spec in section 5.1.2
> > > > > > > > > +        */
> > > > > > > > > +       if (!(features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)))
> > > > > > > > > +               return 0;
> > > > > > > > > +
> > > > > > > > > +       if (features & BIT_ULL(VIRTIO_NET_F_MQ))
> > > > > > > > > +               N = le16_to_cpu(config->max_virtqueue_pairs);
> > > > > > > > > +       else
> > > > > > > > > +               N = 1;
> > > > > > > > > +
> > > > > > > > > +       return nla_put_u16(msg, VDPA_ATTR_DEV_CTRL_VQ_IDX, 2 * N);
> > > > > > > > > +}
> > > > > > > > > +
> > > > > > > > >  static int vdpa_dev_net_mq_config_fill(struct vdpa_device *vdev,
> > > > > > > > >                                        struct sk_buff *msg, u64 features,
> > > > > > > > >                                        const struct virtio_net_config *config)
> > > > > > > > > @@ -730,6 +751,7 @@ static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *ms
> > > > > > > > >         struct virtio_net_config config = {};
> > > > > > > > >         u64 features;
> > > > > > > > >         u16 val_u16;
> > > > > > > > > +       int err;
> > > > > > > > >
> > > > > > > > >         vdpa_get_config(vdev, 0, &config, sizeof(config));
> > > > > > > > >
> > > > > > > > > @@ -746,6 +768,9 @@ static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *ms
> > > > > > > > >                 return -EMSGSIZE;
> > > > > > > > >
> > > > > > > > >         features = vdev->config->get_driver_features(vdev);
> > > > > > > > > +       err = vdpa_dev_net_ctrl_vq_fill(vdev, msg, &config, features);
> > > > > > > > > +       if (err)
> > > > > > > > > +               return err;
> > > > > > > > >
> > > > > > > > >         return vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
> > > > > > > > >  }
> > > > > > > > > diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> > > > > > > > > index a252f06f9dfd..2e3a7f89f42d 100644
> > > > > > > > > --- a/include/uapi/linux/vdpa.h
> > > > > > > > > +++ b/include/uapi/linux/vdpa.h
> > > > > > > > > @@ -34,6 +34,7 @@ enum vdpa_attr {
> > > > > > > > >         VDPA_ATTR_DEV_MAX_VQS,                  /* u32 */
> > > > > > > > >         VDPA_ATTR_DEV_MAX_VQ_SIZE,              /* u16 */
> > > > > > > > >         VDPA_ATTR_DEV_MIN_VQ_SIZE,              /* u16 */
> > > > > > > > > +       VDPA_ATTR_DEV_CTRL_VQ_IDX,              /* u16 */
> > > > > > > > >
> > > > > > > > >         VDPA_ATTR_DEV_NET_CFG_MACADDR,          /* binary */
> > > > > > > > >         VDPA_ATTR_DEV_NET_STATUS,               /* u8 */
> > > > > > > > > --
> > > > > > > > > 2.33.1
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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