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

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

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.

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
>