Re: [PATCH v7 3/3] net: ax88796c: ASIX AX88796C SPI Ethernet Adapter Driver

[Jakub Kicinski]

On Tue, 24 Nov 2020 13:03:30 +0100 Łukasz Stelmach wrote:
> +static int
> +ax88796c_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> +{
> +	struct ax88796c_device *ax_local = to_ax88796c_device(ndev);
> +
> +	skb_queue_tail(&ax_local->tx_wait_q, skb);
> +	if (skb_queue_len(&ax_local->tx_wait_q) > TX_QUEUE_HIGH_WATER) {
> +		netif_err(ax_local, tx_queued, ndev,
> +			  "Too many TX packets in queue %d\n",
> +			  skb_queue_len(&ax_local->tx_wait_q));

This will probably happen under heavy traffic. No need to print errors,
it's normal to back pressure.

> +		netif_stop_queue(ndev);
> +	}
> +
> +	set_bit(EVENT_TX, &ax_local->flags);
> +	schedule_work(&ax_local->ax_work);
> +
> +	return NETDEV_TX_OK;
> +}
> +
> +static void
> +ax88796c_skb_return(struct ax88796c_device *ax_local, struct sk_buff *skb,
> +		    struct rx_header *rxhdr)
> +{
> +	struct net_device *ndev = ax_local->ndev;
> +	int status;
> +
> +	do {
> +		if (!(ndev->features & NETIF_F_RXCSUM))
> +			break;
> +
> +		/* checksum error bit is set */
> +		if ((rxhdr->flags & RX_HDR3_L3_ERR) ||
> +		    (rxhdr->flags & RX_HDR3_L4_ERR))
> +			break;
> +
> +		/* Other types may be indicated by more than one bit. */
> +		if ((rxhdr->flags & RX_HDR3_L4_TYPE_TCP) ||
> +		    (rxhdr->flags & RX_HDR3_L4_TYPE_UDP))
> +			skb->ip_summed = CHECKSUM_UNNECESSARY;
> +	} while (0);
> +
> +	ax_local->stats.rx_packets++;
> +	ax_local->stats.rx_bytes += skb->len;
> +	skb->dev = ndev;
> +
> +	skb->truesize = skb->len + sizeof(struct sk_buff);
> +	skb->protocol = eth_type_trans(skb, ax_local->ndev);
> +
> +	netif_info(ax_local, rx_status, ndev, "< rx, len %zu, type 0x%x\n",
> +		   skb->len + sizeof(struct ethhdr), skb->protocol);
> +
> +	status = netif_rx(skb);

If I'm reading things right this is in process context, so netif_rx_ni()

> +	if (status != NET_RX_SUCCESS)
> +		netif_info(ax_local, rx_err, ndev,
> +			   "netif_rx status %d\n", status);

Again, it's inadvisable to put per packet prints without any rate
limiting in the data path.