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

Jason Wang
2022-04-18T07:50:00Z

On Mon, Apr 18, 2022 at 11:24 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> 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.

Ok, but we need guarantee the memory ordering in this case. Disable RX
napi could be a solution for this.

Thanks

>
> 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
> >
>