Re: [PATCH net-next v2 2/2] virtio_net: get init coalesce value when probe

[Heng Qi <hengqi@linux.alibaba.com>]

On Wed, 8 May 2024 10:22:04 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Tue, May 7, 2024 at 3:01 PM Heng Qi <hengqi@linux.alibaba.com> wrote:
> >
> > On Tue, 7 May 2024 14:24:12 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > > On Fri, Apr 26, 2024 at 2:54 PM Heng Qi <hengqi@linux.alibaba.com> wrote:
> > > >
> > > > Currently, virtio-net lacks a way to obtain the default coalesce
> > > > values of the device during the probe phase. That is, the device
> > > > may have default experience values, but the user uses "ethtool -c"
> > > > to query that the values are still 0.
> > > >
> > > > Therefore, we reuse VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET to complete the goal.
> > > >
> > > > Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> > > > ---
> > > >  drivers/net/virtio_net.c | 68 +++++++++++++++++++++++++++++++++++-----
> > > >  1 file changed, 61 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index 3bc9b1e621db..fe0c15819dd3 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -4623,6 +4623,46 @@ static int virtnet_validate(struct virtio_device *vdev)
> > > >         return 0;
> > > >  }
> > > >
> > > > +static int virtnet_get_coal_init_value(struct virtnet_info *vi,
> > > > +                                      u16 _vqn, bool is_tx)
> > > > +{
> > > > +       struct virtio_net_ctrl_coal *coal = &vi->ctrl->coal_vq.coal;
> > > > +       __le16 *vqn = &vi->ctrl->coal_vq.vqn;
> > > > +       struct scatterlist sgs_in, sgs_out;
> > > > +       u32 usecs, pkts, i;
> > > > +       bool ret;
> > > > +
> > > > +       *vqn = cpu_to_le16(_vqn);
> > > > +
> > > > +       sg_init_one(&sgs_out, vqn, sizeof(*vqn));
> > > > +       sg_init_one(&sgs_in, coal, sizeof(*coal));
> > > > +       ret = virtnet_send_command_reply(vi, VIRTIO_NET_CTRL_NOTF_COAL,
> > > > +                                        VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET,
> > > > +                                        &sgs_out, &sgs_in);
> > > > +       if (!ret)
> > > > +               return ret;
> > > > +
> > > > +       usecs = le32_to_cpu(coal->max_usecs);
> > > > +       pkts = le32_to_cpu(coal->max_packets);
> > > > +       if (is_tx) {
> > > > +               vi->intr_coal_tx.max_usecs = usecs;
> > > > +               vi->intr_coal_tx.max_packets = pkts;
> > > > +               for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > +                       vi->sq[i].intr_coal.max_usecs = usecs;
> > > > +                       vi->sq[i].intr_coal.max_packets = pkts;
> > > > +               }
> > > > +       } else {
> > > > +               vi->intr_coal_rx.max_usecs = usecs;
> > > > +               vi->intr_coal_rx.max_packets = pkts;
> > > > +               for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > +                       vi->rq[i].intr_coal.max_usecs = usecs;
> > > > +                       vi->rq[i].intr_coal.max_packets = pkts;
> > > > +               }
> > > > +       }
> > > > +
> > > > +       return 0;
> > > > +}
> > > > +
> > > >  static bool virtnet_check_guest_gso(const struct virtnet_info *vi)
> > > >  {
> > > >         return virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> > > > @@ -4885,13 +4925,6 @@ static int virtnet_probe(struct virtio_device *vdev)
> > > >                         vi->intr_coal_tx.max_packets = 0;
> > > >         }
> > > >
> > > > -       if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
> > > > -               /* The reason is the same as VIRTIO_NET_F_NOTF_COAL. */
> > > > -               for (i = 0; i < vi->max_queue_pairs; i++)
> > > > -                       if (vi->sq[i].napi.weight)
> > > > -                               vi->sq[i].intr_coal.max_packets = 1;
> > > > -       }
> > > > -
> > > >  #ifdef CONFIG_SYSFS
> > > >         if (vi->mergeable_rx_bufs)
> > > >                 dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
> > > > @@ -4926,6 +4959,27 @@ static int virtnet_probe(struct virtio_device *vdev)
> > > >
> > > >         virtio_device_ready(vdev);
> > > >
> > > > +       if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
> > > > +               /* The reason is the same as VIRTIO_NET_F_NOTF_COAL. */
> > > > +               for (i = 0; i < vi->max_queue_pairs; i++)
> > > > +                       if (vi->sq[i].napi.weight)
> > > > +                               vi->sq[i].intr_coal.max_packets = 1;
> > > > +
> > > > +               /* The loop exits if the default value from any
> > > > +                * queue is successfully read.
> > > > +                */
> > >
> > > So this assumes the default values are the same. Is this something
> > > required by the spec? If not, we probably need to iterate all the
> > > queues.
> > >
> >
> > From internal practice, and from the default behavior of other existing drivers,
> > the queues all have the same value at the beginning, so here it seems feasible
> > that we get the value of queue 0 to represent the global value instead of using
> > a loop.
> 
> Well, unless the spec says the values are equal, the driver needs to iterate.

Ok. Will update this in the next version.

Thanks.

> 
> >
> > Moreover, obtaining the value once for each queue initially does not seem to be
> > very friendly for devices with a large number of queues.
> 
> We probably don't care too much about the time spent on the probe. For
> example, there would be a lot of registers read/write as well.
> 
> Thanks
> 
> >
> > Thanks.
> >
> > > Thanks
> > >
> > >
> > > > +               for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > +                       err = virtnet_get_coal_init_value(vi, rxq2vq(i), false);
> > > > +                       if (!err)
> > > > +                               break;
> > > > +               }
> > > > +               for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > +                       err = virtnet_get_coal_init_value(vi, txq2vq(i), true);
> > > > +                       if (!err)
> > > > +                               break;
> > > > +               }
> > > > +       }
> > > > +
> > > >         _virtnet_set_queues(vi, vi->curr_queue_pairs);
> > > >
> > > >         /* a random MAC address has been assigned, notify the device.
> > > > --
> > > > 2.32.0.3.g01195cf9f
> > > >
> > >
> >
>