Re: [net-next 01/12] net/mlx5e: Add UDP GSO support

[Boris Pismenny <borisp@mellanox.com>]

On 06/30/18 01:19, Willem de Bruijn wrote:
> On Fri, Jun 29, 2018 at 2:24 AM Saeed Mahameed <saeedm@mellanox.com> wrote:
>> From: Boris Pismenny <borisp@mellanox.com>
>>
>> This patch enables UDP GSO support. We enable this by using two WQEs
>> the first is a UDP LSO WQE for all segments with equal length, and the
>> second is for the last segment in case it has different length.
>> Due to HW limitation, before sending, we must adjust the packet length fields.
>>
>> We measure performance between two Intel(R) Xeon(R) CPU E5-2643 v2 @3.50GHz
>> machines connected back-to-back with Connectx4-Lx (40Gbps) NICs.
>> We compare single stream UDP, UDP GSO and UDP GSO with offload.
>> Performance:
>>                  | MSS (bytes)   | Throughput (Gbps)     | CPU utilization (%)
>> UDP GSO offload | 1472          | 35.6                  | 8%
>> UDP GSO         | 1472          | 25.5                  | 17%
>> UDP             | 1472          | 10.2                  | 17%
>> UDP GSO offload | 1024          | 35.6                  | 8%
>> UDP GSO         | 1024          | 19.2                  | 17%
>> UDP             | 1024          | 5.7                   | 17%
>> UDP GSO offload | 512           | 33.8                  | 16%
>> UDP GSO         | 512           | 10.4                  | 17%
>> UDP             | 512           | 3.5                   | 17%
> Very nice results :)
Thanks. We expect to have 100Gbps results by netdev0x12.

>> +static void mlx5e_udp_gso_prepare_last_skb(struct sk_buff *skb,
>> +                                          struct sk_buff *nskb,
>> +                                          int remaining)
>> +{
>> +       int bytes_needed = remaining, remaining_headlen, remaining_page_offset;
>> +       int headlen = skb_transport_offset(skb) + sizeof(struct udphdr);
>> +       int payload_len = remaining + sizeof(struct udphdr);
>> +       int k = 0, i, j;
>> +
>> +       skb_copy_bits(skb, 0, nskb->data, headlen);
>> +       nskb->dev = skb->dev;
>> +       skb_reset_mac_header(nskb);
>> +       skb_set_network_header(nskb, skb_network_offset(skb));
>> +       skb_set_transport_header(nskb, skb_transport_offset(skb));
>> +       skb_set_tail_pointer(nskb, headlen);
>> +
>> +       /* How many frags do we need? */
>> +       for (i = skb_shinfo(skb)->nr_frags - 1; i >= 0; i--) {
>> +               bytes_needed -= skb_frag_size(&skb_shinfo(skb)->frags[i]);
>> +               k++;
>> +               if (bytes_needed <= 0)
>> +                       break;
>> +       }
>> +
>> +       /* Fill the first frag and split it if necessary */
>> +       j = skb_shinfo(skb)->nr_frags - k;
>> +       remaining_page_offset = -bytes_needed;
>> +       skb_fill_page_desc(nskb, 0,
>> +                          skb_shinfo(skb)->frags[j].page.p,
>> +                          skb_shinfo(skb)->frags[j].page_offset + remaining_page_offset,
>> +                          skb_shinfo(skb)->frags[j].size - remaining_page_offset);
>> +
>> +       skb_frag_ref(skb, j);
>> +
>> +       /* Fill the rest of the frags */
>> +       for (i = 1; i < k; i++) {
>> +               j = skb_shinfo(skb)->nr_frags - k + i;
>> +
>> +               skb_fill_page_desc(nskb, i,
>> +                                  skb_shinfo(skb)->frags[j].page.p,
>> +                                  skb_shinfo(skb)->frags[j].page_offset,
>> +                                  skb_shinfo(skb)->frags[j].size);
>> +               skb_frag_ref(skb, j);
>> +       }
>> +       skb_shinfo(nskb)->nr_frags = k;
>> +
>> +       remaining_headlen = remaining - skb->data_len;
>> +
>> +       /* headlen contains remaining data? */
>> +       if (remaining_headlen > 0)
>> +               skb_copy_bits(skb, skb->len - remaining, nskb->data + headlen,
>> +                             remaining_headlen);
>> +       nskb->len = remaining + headlen;
>> +       nskb->data_len =  payload_len - sizeof(struct udphdr) +
>> +               max_t(int, 0, remaining_headlen);
>> +       nskb->protocol = skb->protocol;
>> +       if (nskb->protocol == htons(ETH_P_IP)) {
>> +               ip_hdr(nskb)->id = htons(ntohs(ip_hdr(nskb)->id) +
>> +                                        skb_shinfo(skb)->gso_segs);
>> +               ip_hdr(nskb)->tot_len =
>> +                       htons(payload_len + sizeof(struct iphdr));
>> +       } else {
>> +               ipv6_hdr(nskb)->payload_len = htons(payload_len);
>> +       }
>> +       udp_hdr(nskb)->len = htons(payload_len);
>> +       skb_shinfo(nskb)->gso_size = 0;
>> +       nskb->ip_summed = skb->ip_summed;
>> +       nskb->csum_start = skb->csum_start;
>> +       nskb->csum_offset = skb->csum_offset;
>> +       nskb->queue_mapping = skb->queue_mapping;
>> +}
>> +
>> +/* might send skbs and update wqe and pi */
>> +struct sk_buff *mlx5e_udp_gso_handle_tx_skb(struct net_device *netdev,
>> +                                           struct mlx5e_txqsq *sq,
>> +                                           struct sk_buff *skb,
>> +                                           struct mlx5e_tx_wqe **wqe,
>> +                                           u16 *pi)
>> +{
>> +       int payload_len = skb_shinfo(skb)->gso_size + sizeof(struct udphdr);
>> +       int headlen = skb_transport_offset(skb) + sizeof(struct udphdr);
>> +       int remaining = (skb->len - headlen) % skb_shinfo(skb)->gso_size;
>> +       struct sk_buff *nskb;
>> +
>> +       if (skb->protocol == htons(ETH_P_IP))
>> +               ip_hdr(skb)->tot_len = htons(payload_len + sizeof(struct iphdr));
>> +       else
>> +               ipv6_hdr(skb)->payload_len = htons(payload_len);
>> +       udp_hdr(skb)->len = htons(payload_len);
>> +       if (!remaining)
>> +               return skb;
>> +
>> +       nskb = alloc_skb(max_t(int, headlen, headlen + remaining - skb->data_len), GFP_ATOMIC);
>> +       if (unlikely(!nskb)) {
>> +               sq->stats->dropped++;
>> +               return NULL;
>> +       }
>> +
>> +       mlx5e_udp_gso_prepare_last_skb(skb, nskb, remaining);
>> +
>> +       skb_shinfo(skb)->gso_segs--;
>> +       pskb_trim(skb, skb->len - remaining);
>> +       mlx5e_sq_xmit(sq, skb, *wqe, *pi);
>> +       mlx5e_sq_fetch_wqe(sq, wqe, pi);
>> +       return nskb;
>> +}
> The device driver seems to be implementing the packet split here
> similar to NETIF_F_GSO_PARTIAL. When advertising the right flag, the
> stack should be able to do that for you and pass two packets to the
> driver.

We've totally missed that!
Thank you. I'll fix and resubmit.