RE: [PATCH V2 net 2/4] net: fec: recycle pages for transmitted XDP frames

[Wei Fang]

> -----Original Message-----
> From: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
> Sent: 2023年7月6日 19:59
> To: Wei Fang <wei.fang@xxxxxxx>
> Cc: davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> pabeni@xxxxxxxxxx; ast@xxxxxxxxxx; daniel@xxxxxxxxxxxxx;
> hawk@xxxxxxxxxx; john.fastabend@xxxxxxxxx; Shenwei Wang
> <shenwei.wang@xxxxxxx>; Clark Wang <xiaoning.wang@xxxxxxx>;
> netdev@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>;
> linux-kernel@xxxxxxxxxxxxxxx; bpf@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH V2 net 2/4] net: fec: recycle pages for transmitted XDP
> frames
> 
> From: Wei Fang <wei.fang@xxxxxxx>
> Date: Thu,  6 Jul 2023 16:10:10 +0800
> 
> > From: Wei Fang <wei.fang@xxxxxxx>
> >
> > Once the XDP frames have been successfully transmitted through the
> > ndo_xdp_xmit() interface, it's the driver responsibility to free the
> > frames so that the page_pool can recycle the pages and reuse them.
> > However, this action is not implemented in the fec driver.
> > This leads to a user-visible problem that the console will print the
> > following warning log.
> 
> [...]
> 
> > +				if (txq->tx_buf[i].xdp) {
> > +					xdp_return_frame(txq->tx_buf[i].xdp);
> > +					txq->tx_buf[i].xdp = NULL;
> > +				}
> > +
> > +				/* restore default tx buffer type: FEC_TXBUF_T_SKB */
> > +				txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
> 
> Here and in the related places below: maybe set ::type dynamically when
> sending to either SKB or XDP instead of setting it only for XDP and then
> restoring each time?
I also considered this method. but when the skb has frags or needs to be TSO,
only the last tx_buf of the skb needs to store the skb pointer, but all the tx_buf
of the skb needs to set the type explicitly, I think it is a bit mess and not concise.
So I restore the type to default when recycle the BDs. Anyway, it;s just a difference
in implement, if you guys insist it's better to set the type explicitly, I will modify
the patch. Thanks!
> 
> >  			}
> > +
> >  			bdp->cbd_bufaddr = cpu_to_fec32(0);
> >  			bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
> >  		}
> [...]
> 
> Thanks,
> Olek