Re: [PATCH v9 31/32] virtio_net: support rx/tx queue resize

Xuan Zhuo
2022-04-18T03:24:18Z

On Wed, 13 Apr 2022 16:00:18 +0800, Jason Wang <jasowang@redhat.com> wrote:
>
> 在 2022/4/6 上午11:43, Xuan Zhuo 写道:
> > This patch implements the resize function of the rx, tx queues.
> > Based on this function, it is possible to modify the ring num of the
> > queue.
> >
> > There may be an exception during the resize process, the resize may
> > fail, or the vq can no longer be used. Either way, we must execute
> > napi_enable(). Because napi_disable is similar to a lock, napi_enable
> > must be called after calling napi_disable.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> > drivers/net/virtio_net.c | 81 ++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 81 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index b8bf00525177..ba6859f305f7 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -251,6 +251,9 @@ struct padded_vnet_hdr {
> > char padding[4];
> > };
> >
> > +static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> > +static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf);
> > +
> > static bool is_xdp_frame(void *ptr)
> > {
> > return (unsigned long)ptr & VIRTIO_XDP_FLAG;
> > @@ -1369,6 +1372,15 @@ static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
> > {
> > napi_enable(napi);
> >
> > + /* Check if vq is in reset state. The normal reset/resize process will
> > + * be protected by napi. However, the protection of napi is only enabled
> > + * during the operation, and the protection of napi will end after the
> > + * operation is completed. If re-enable fails during the process, vq
> > + * will remain unavailable with reset state.
> > + */
> > + if (vq->reset)
> > + return;
>
>
> I don't get when could we hit this condition.
>
>
> > +
> > /* If all buffers were filled by other side before we napi_enabled, we
> > * won't get another interrupt, so process any outstanding packets now.
> > * Call local_bh_enable after to trigger softIRQ processing.
> > @@ -1413,6 +1425,15 @@ static void refill_work(struct work_struct *work)
> > struct receive_queue *rq = &vi->rq[i];
> >
> > napi_disable(&rq->napi);
> > +
> > + /* Check if vq is in reset state. See more in
> > + * virtnet_napi_enable()
> > + */
> > + if (rq->vq->reset) {
> > + virtnet_napi_enable(rq->vq, &rq->napi);
> > + continue;
> > + }
>
>
> Can we do something similar in virtnet_close() by canceling the work?
>
>
> > +
> > still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
> > virtnet_napi_enable(rq->vq, &rq->napi);
> >
> > @@ -1523,6 +1544,10 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
> > if (!sq->napi.weight || is_xdp_raw_buffer_queue(vi, index))
> > return;
> >
> > + /* Check if vq is in reset state. See more in virtnet_napi_enable() */
> > + if (sq->vq->reset)
> > + return;
>
>
> We've disabled TX napi, any chance we can still hit this?

static int virtnet_poll(struct napi_struct *napi, int budget)
{
struct receive_queue *rq =
container_of(napi, struct receive_queue, napi);
struct virtnet_info *vi = rq->vq->vdev->priv;
struct send_queue *sq;
unsigned int received;
unsigned int xdp_xmit = 0;

virtnet_poll_cleantx(rq);
...
}

This is called by rx poll. Although it is the logic of tx, it is not driven by
tx napi, but is called in rx poll.

Thanks.

>
>
> > +
> > if (__netif_tx_trylock(txq)) {
> > do {
> > virtqueue_disable_cb(sq->vq);
> > @@ -1769,6 +1794,62 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> > return NETDEV_TX_OK;
> > }
> >
> > +static int virtnet_rx_resize(struct virtnet_info *vi,
> > + struct receive_queue *rq, u32 ring_num)
> > +{
> > + int err;
> > +
> > + napi_disable(&rq->napi);
> > +
> > + err = virtqueue_resize(rq->vq, ring_num, virtnet_rq_free_unused_buf);
> > + if (err)
> > + goto err;
> > +
> > + if (!try_fill_recv(vi, rq, GFP_KERNEL))
> > + schedule_delayed_work(&vi->refill, 0);
> > +
> > + virtnet_napi_enable(rq->vq, &rq->napi);
> > + return 0;
> > +
> > +err:
> > + netdev_err(vi->dev,
> > + "reset rx reset vq fail: rx queue index: %td err: %d\n",
> > + rq - vi->rq, err);
> > + virtnet_napi_enable(rq->vq, &rq->napi);
> > + return err;
> > +}
> > +
> > +static int virtnet_tx_resize(struct virtnet_info *vi,
> > + struct send_queue *sq, u32 ring_num)
> > +{
> > + struct netdev_queue *txq;
> > + int err, qindex;
> > +
> > + qindex = sq - vi->sq;
> > +
> > + virtnet_napi_tx_disable(&sq->napi);
> > +
> > + txq = netdev_get_tx_queue(vi->dev, qindex);
> > + __netif_tx_lock_bh(txq);
> > + netif_stop_subqueue(vi->dev, qindex);
> > + __netif_tx_unlock_bh(txq);
> > +
> > + err = virtqueue_resize(sq->vq, ring_num, virtnet_sq_free_unused_buf);
> > + if (err)
> > + goto err;
> > +
> > + netif_start_subqueue(vi->dev, qindex);
> > + virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
> > + return 0;
> > +
> > +err:
>
>
> I guess we can still start the queue in this case? (Since we don't
> change the queue if resize fails).
>
>
> > + netdev_err(vi->dev,
> > + "reset tx reset vq fail: tx queue index: %td err: %d\n",
> > + sq - vi->sq, err);
> > + virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
> > + return err;
> > +}
> > +
> > /*
> > * Send command via the control virtqueue and check status. Commands
> > * supported by the hypervisor, as indicated by feature bits, should
>