RE: [PATCH net-next] net: fec: add XDP_TX feature support

[Wei Fang]

> -----Original Message-----
> From: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
> Sent: 2023年7月18日 23:15
> To: Wei Fang <wei.fang@xxxxxxx>
> Cc: davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> pabeni@xxxxxxxxxx; ast@xxxxxxxxxx; daniel@xxxxxxxxxxxxx;
> hawk@xxxxxxxxxx; john.fastabend@xxxxxxxxx; Clark Wang
> <xiaoning.wang@xxxxxxx>; Shenwei Wang <shenwei.wang@xxxxxxx>;
> netdev@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>;
> linux-kernel@xxxxxxxxxxxxxxx; bpf@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH net-next] net: fec: add XDP_TX feature support
> 
> From: Wei Fang <wei.fang@xxxxxxx>
> Date: Mon, 17 Jul 2023 18:37:09 +0800
> 
> > The XDP_TX feature is not supported before, and all the frames which
> > are deemed to do XDP_TX action actually do the XDP_DROP action. So
> > this patch adds the XDP_TX support to FEC driver.
> 
> [...]
> 
> > @@ -3897,6 +3923,29 @@ static int fec_enet_txq_xmit_frame(struct
> fec_enet_private *fep,
> >  	return 0;
> >  }
> >
> > +static int fec_enet_xdp_tx_xmit(struct net_device *ndev,
> > +				struct xdp_buff *xdp)
> > +{
> > +	struct xdp_frame *xdpf = xdp_convert_buff_to_frame(xdp);
> 
> Have you tried avoid converting buff to frame in case of XDP_TX? It would save
> you a bunch of CPU cycles.
> 
Sorry, I haven't. I referred to several ethernet drivers about the implementation of
XDP_TX. Most drivers adopt the method of converting xdp_buff to xdp_frame, and
in this method, I can reuse the existing interface fec_enet_txq_xmit_frame() to
transmit the frames and the implementation is relatively simple. Otherwise, there
will be more changes and more effort is needed to implement this feature.
Thanks!

> > +	struct fec_enet_private *fep = netdev_priv(ndev);
> > +	struct fec_enet_priv_tx_q *txq;
> > +	int cpu = smp_processor_id();
> > +	struct netdev_queue *nq;
> > +	int queue, ret;
> > +
> > +	queue = fec_enet_xdp_get_tx_queue(fep, cpu);
> > +	txq = fep->tx_queue[queue];
> > +	nq = netdev_get_tx_queue(fep->netdev, queue);
> > +
> > +	__netif_tx_lock(nq, cpu);
> > +
> > +	ret = fec_enet_txq_xmit_frame(fep, txq, xdpf, false);
> > +
> > +	__netif_tx_unlock(nq);
> > +
> > +	return ret;
> > +}
> > +
> >  static int fec_enet_xdp_xmit(struct net_device *dev,
> >  			     int num_frames,
> >  			     struct xdp_frame **frames,
> > @@ -3917,7 +3966,7 @@ static int fec_enet_xdp_xmit(struct net_device
> *dev,
> >  	__netif_tx_lock(nq, cpu);
> >
> >  	for (i = 0; i < num_frames; i++) {
> > -		if (fec_enet_txq_xmit_frame(fep, txq, frames[i]) < 0)
> > +		if (fec_enet_txq_xmit_frame(fep, txq, frames[i], true) < 0)
> >  			break;
> >  		sent_frames++;
> >  	}
>