Re: [PATCH v6 net-next 15/19] ionic: Add Tx and Rx handling

[Jakub Kicinski <jakub.kicinski@netronome.com>]

On Thu, 29 Aug 2019 11:27:16 -0700, Shannon Nelson wrote:
> +static int ionic_tx_tso(struct ionic_queue *q, struct sk_buff *skb)
> +{
> +	struct ionic_tx_stats *stats = q_to_tx_stats(q);
> +	struct ionic_desc_info *abort = q->head;
> +	struct device *dev = q->lif->ionic->dev;
> +	struct ionic_desc_info *rewind = abort;
> +	struct ionic_txq_sg_elem *elem;
> +	struct ionic_txq_desc *desc;
> +	unsigned int frag_left = 0;
> +	unsigned int offset = 0;
> +	unsigned int len_left;
> +	dma_addr_t desc_addr;
> +	unsigned int hdrlen;
> +	unsigned int nfrags;
> +	unsigned int seglen;
> +	u64 total_bytes = 0;
> +	u64 total_pkts = 0;
> +	unsigned int left;
> +	unsigned int len;
> +	unsigned int mss;
> +	skb_frag_t *frag;
> +	bool start, done;
> +	bool outer_csum;
> +	bool has_vlan;
> +	u16 desc_len;
> +	u8 desc_nsge;
> +	u16 vlan_tci;
> +	bool encap;
> +	int err;
> +
> +	mss = skb_shinfo(skb)->gso_size;
> +	nfrags = skb_shinfo(skb)->nr_frags;
> +	len_left = skb->len - skb_headlen(skb);
> +	outer_csum = (skb_shinfo(skb)->gso_type & SKB_GSO_GRE_CSUM) ||
> +		     (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_TUNNEL_CSUM);
> +	has_vlan = !!skb_vlan_tag_present(skb);
> +	vlan_tci = skb_vlan_tag_get(skb);
> +	encap = skb->encapsulation;
> +
> +	/* Preload inner-most TCP csum field with IP pseudo hdr
> +	 * calculated with IP length set to zero.  HW will later
> +	 * add in length to each TCP segment resulting from the TSO.
> +	 */
> +
> +	if (encap)
> +		err = ionic_tx_tcp_inner_pseudo_csum(skb);
> +	else
> +		err = ionic_tx_tcp_pseudo_csum(skb);
> +	if (err)
> +		return err;
> +
> +	if (encap)
> +		hdrlen = skb_inner_transport_header(skb) - skb->data +
> +			 inner_tcp_hdrlen(skb);
> +	else
> +		hdrlen = skb_transport_offset(skb) + tcp_hdrlen(skb);
> +
> +	seglen = hdrlen + mss;
> +	left = skb_headlen(skb);
> +
> +	desc = ionic_tx_tso_next(q, &elem);
> +	start = true;
> +
> +	/* Chop skb->data up into desc segments */
> +
> +	while (left > 0) {
> +		len = min(seglen, left);
> +		frag_left = seglen - len;
> +		desc_addr = ionic_tx_map_single(q, skb->data + offset, len);
> +		if (dma_mapping_error(dev, desc_addr))
> +			goto err_out_abort;
> +		desc_len = len;
> +		desc_nsge = 0;
> +		left -= len;
> +		offset += len;
> +		if (nfrags > 0 && frag_left > 0)
> +			continue;
> +		done = (nfrags == 0 && left == 0);
> +		ionic_tx_tso_post(q, desc, skb,
> +				  desc_addr, desc_nsge, desc_len,
> +				  hdrlen, mss,
> +				  outer_csum,
> +				  vlan_tci, has_vlan,
> +				  start, done);
> +		total_pkts++;
> +		total_bytes += start ? len : len + hdrlen;
> +		desc = ionic_tx_tso_next(q, &elem);
> +		start = false;
> +		seglen = mss;
> +	}
> +
> +	/* Chop skb frags into desc segments */
> +
> +	for (frag = skb_shinfo(skb)->frags; len_left; frag++) {
> +		offset = 0;
> +		left = skb_frag_size(frag);
> +		len_left -= left;
> +		nfrags--;
> +		stats->frags++;
> +
> +		while (left > 0) {
> +			if (frag_left > 0) {
> +				len = min(frag_left, left);
> +				frag_left -= len;
> +				elem->addr =
> +				    cpu_to_le64(ionic_tx_map_frag(q, frag,
> +								  offset, len));
> +				if (dma_mapping_error(dev, elem->addr))
> +					goto err_out_abort;
> +				elem->len = cpu_to_le16(len);
> +				elem++;
> +				desc_nsge++;
> +				left -= len;
> +				offset += len;
> +				if (nfrags > 0 && frag_left > 0)
> +					continue;
> +				done = (nfrags == 0 && left == 0);
> +				ionic_tx_tso_post(q, desc, skb, desc_addr,
> +						  desc_nsge, desc_len,
> +						  hdrlen, mss, outer_csum,
> +						  vlan_tci, has_vlan,
> +						  start, done);
> +				total_pkts++;
> +				total_bytes += start ? len : len + hdrlen;
> +				desc = ionic_tx_tso_next(q, &elem);
> +				start = false;
> +			} else {
> +				len = min(mss, left);
> +				frag_left = mss - len;
> +				desc_addr = ionic_tx_map_frag(q, frag,
> +							      offset, len);
> +				if (dma_mapping_error(dev, desc_addr))
> +					goto err_out_abort;
> +				desc_len = len;
> +				desc_nsge = 0;
> +				left -= len;
> +				offset += len;
> +				if (nfrags > 0 && frag_left > 0)
> +					continue;
> +				done = (nfrags == 0 && left == 0);
> +				ionic_tx_tso_post(q, desc, skb, desc_addr,
> +						  desc_nsge, desc_len,
> +						  hdrlen, mss, outer_csum,
> +						  vlan_tci, has_vlan,
> +						  start, done);
> +				total_pkts++;
> +				total_bytes += start ? len : len + hdrlen;
> +				desc = ionic_tx_tso_next(q, &elem);
> +				start = false;
> +			}
> +		}
> +	}
> +
> +	stats->pkts += total_pkts;
> +	stats->bytes += total_bytes;
> +	stats->tso++;
> +
> +	return 0;
> +
> +err_out_abort:
> +	while (rewind->desc != q->head->desc) {
> +		ionic_tx_clean(q, rewind, NULL, NULL);
> +		rewind = rewind->next;
> +	}
> +	q->head = abort;
> +
> +	return -ENOMEM;
> +}

There's definitely a function for helping drivers which can't do full
TSO slice up the packet, but I can't find it now 😫😫

Eric would definitely know.

Did you have a look? Would it be useful here?