netdev - Re: [PATCH net-next] net: fec: add XDP

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Date: Wed, 19 Jul 2023 20:45:53 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Wei Fang <wei.fang@....com>
Cc: davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
 john.fastabend@...il.com, xiaoning.wang@....com, shenwei.wang@....com,
 netdev@...r.kernel.org, linux-imx@....com, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH net-next] net: fec: add XDP_TX feature support

On Mon, 17 Jul 2023 18:37:09 +0800 Wei Fang wrote:
> -			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);

Are you taking budget into account? When NAPI is called with budget 
of 0 we are *not* in napi / softirq context. You can't be processing
any XDP tx under such conditions (it may be a netpoll call from IRQ
context).

> +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);
> +	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);

If you're reusing the same queues as the stack you need to call
txq_trans_cond_update() at some point, otherwise the stack may
print a splat complaining the queue got stuck.
-- 
pw-bot: cr