netdev - RE: [PATCH V2 net-next] net: fec: add XDP

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Date: Tue, 25 Jul 2023 01:58:56 +0000
From: Wei Fang <wei.fang@....com>
To: Jakub Kicinski <kuba@...nel.org>
CC: "davem@...emloft.net" <davem@...emloft.net>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "pabeni@...hat.com" <pabeni@...hat.com>, Shenwei Wang
	<shenwei.wang@....com>, Clark Wang <xiaoning.wang@....com>, "ast@...nel.org"
	<ast@...nel.org>, "daniel@...earbox.net" <daniel@...earbox.net>,
	"hawk@...nel.org" <hawk@...nel.org>, "john.fastabend@...il.com"
	<john.fastabend@...il.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, dl-linux-imx <linux-imx@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: RE: [PATCH V2 net-next] net: fec: add XDP_TX feature support

> On Fri, 21 Jul 2023 14:21:53 +0800 Wei Fang wrote:
> > +			/* Tx processing cannot call any XDP (or page pool) APIs if
> > +			 * the "budget" is 0. Because NAPI is called with budget of
> > +			 * 0 (such as netpoll) indicates we may be in an IRQ context,
> > +			 * however, we can't use the page pool from IRQ context.
> > +			 */
> > +			if (unlikely(!budget))
> > +				break;
> > +
> >  			xdpf = txq->tx_buf[index].xdp;
> > -			if (bdp->cbd_bufaddr)
> > +			if (bdp->cbd_bufaddr &&
> > +			    txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO)
> >  				dma_unmap_single(&fep->pdev->dev,
> >  						 fec32_to_cpu(bdp->cbd_bufaddr),
> >  						 fec16_to_cpu(bdp->cbd_datlen), @@ -1474,7
> +1486,10 @@
> > fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
> >  			/* Free the sk buffer associated with this last transmit */
> >  			dev_kfree_skb_any(skb);
> >  		} else {
> > -			xdp_return_frame(xdpf);
> > +			if (txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO)
> > +				xdp_return_frame(xdpf);
> > +			else
> > +				xdp_return_frame_rx_napi(xdpf);
> 
> I think that you need to also break if (!budget) here,
I think there is no need to break again here, because if the "budget" is 0, the code logic
will no jump here.

> xdp_return_frame() may call page pool APIs to return the frame to a page pool
> owned by another driver. And that needs to be fixed in net/main already?
Yes, you are right, I should fixed it in net tree first, and when the fix is merged
into net-next tree, I will send a 3rd version of this patch.