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Date: Fri, 29 Jun 2018 18:19:02 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Saeed Mahameed <saeedm@...lanox.com>
Cc: David Miller <davem@...emloft.net>,
Network Development <netdev@...r.kernel.org>,
ogerlitz@...lanox.com, borisp@...lanox.com, yossiku@...lanox.com,
Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [net-next 01/12] net/mlx5e: Add UDP GSO support
On Fri, Jun 29, 2018 at 2:24 AM Saeed Mahameed <saeedm@...lanox.com> wrote:
>
> From: Boris Pismenny <borisp@...lanox.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 :)
> +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.
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