Re: [PATCH v11 39/40] virtio_net: support tx queue resize

Jason Wang
2022-07-08T06:24:17Z

On Tue, Jul 5, 2022 at 10:01 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Mon, 4 Jul 2022 11:45:52 +0800, Jason Wang <jasowang@redhat.com> wrote:
> >
> > 在 2022/6/29 14:56, Xuan Zhuo 写道:
> > > This patch implements the resize function of the tx queues.
> > > Based on this function, it is possible to modify the ring num of the
> > > queue.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > ---
> > > drivers/net/virtio_net.c | 48 ++++++++++++++++++++++++++++++++++++++++
> > > 1 file changed, 48 insertions(+)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 6ab16fd193e5..fd358462f802 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -135,6 +135,9 @@ struct send_queue {
> > > struct virtnet_sq_stats stats;
> > >
> > > struct napi_struct napi;
> > > +
> > > + /* Record whether sq is in reset state. */
> > > + bool reset;
> > > };
> > >
> > > /* Internal representation of a receive virtqueue */
> > > @@ -279,6 +282,7 @@ struct padded_vnet_hdr {
> > > };
> > >
> > > static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf);
> > > +static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> > >
> > > static bool is_xdp_frame(void *ptr)
> > > {
> > > @@ -1603,6 +1607,11 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
> > > return;
> > >
> > > if (__netif_tx_trylock(txq)) {
> > > + if (READ_ONCE(sq->reset)) {
> > > + __netif_tx_unlock(txq);
> > > + return;
> > > + }
> > > +
> > > do {
> > > virtqueue_disable_cb(sq->vq);
> > > free_old_xmit_skbs(sq, true);
> > > @@ -1868,6 +1877,45 @@ static int virtnet_rx_resize(struct virtnet_info *vi,
> > > 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);
> > > +
> > > + /* 1. wait all ximt complete
> > > + * 2. fix the race of netif_stop_subqueue() vs netif_start_subqueue()
> > > + */
> > > + __netif_tx_lock_bh(txq);
> > > +
> > > + /* Prevent rx poll from accessing sq. */
> > > + WRITE_ONCE(sq->reset, true);
> >
> >
> > Can we simply disable RX NAPI here?
>
> Disable rx napi is indeed a simple solution. But I hope that when dealing with
> tx, it will not affect rx.

Ok, but I think we've already synchronized with tx lock here, isn't it?

Thanks

>
> Thanks.
>
>
> >
> > Thanks
> >
> >
> > > +
> > > + /* Prevent the upper layer from trying to send packets. */
> > > + 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)
> > > + netdev_err(vi->dev, "resize tx fail: tx queue index: %d err: %d\n", qindex, err);
> > > +
> > > + /* Memory barrier before set reset and start subqueue. */
> > > + smp_mb();
> > > +
> > > + WRITE_ONCE(sq->reset, false);
> > > + netif_tx_wake_queue(txq);
> > > +
> > > + 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
> >
>