Re: [PATCH net-next] net/mlx4_en: optimizes get_fixed_ipv6_csum()

[Tariq Toukan]

On 27/04/2018 1:56 AM, Saeed Mahameed wrote:

On Thu, 2018-04-19 at 08:49 -0700, Eric Dumazet wrote:

While trying to support CHECKSUM_COMPLETE for IPV6 fragments,
I had to experiments various hacks in get_fixed_ipv6_csum().
I must admit I could not find how to implement this :/

However, get_fixed_ipv6_csum() does a lot of redundant operations,
calling csum_partial() twice.

First csum_partial() computes the checksum of saddr and daddr,
put in @csum_pseudo_hdr. Undone later in the second csum_partial()
computed on whole ipv6 header.

Then nexthdr is added once, added a second time, then substracted.

payload_len is added once, then substracted.

Really all this can be reduced to two add_csum(), to add back 6 bytes
that were removed by mlx4 when providing hw_checksum in RX
descriptor.

Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Saeed Mahameed <sae...@mellanox.com>
Cc: Tariq Toukan <tar...@mellanox.com>
---
Note: This patch, like other mlx4 patches can definitely wait
Tariq approval, thanks !

LGTM,

Reviewed-by: Saeed Mahameed <sae...@mellanox.com>

Acked-by: Tariq Toukan <tar...@mellanox.com>

Thanks Eric.

  drivers/net/ethernet/mellanox/mlx4/en_rx.c | 21 ++++++++----------
---
  1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index
5c613c6663da51a4ae792eeb4d8956b54655786b..38c56fb6e5f5970f245dd56c38e
1fc63a9349a07 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
@@ -593,30 +593,25 @@ static int get_fixed_ipv4_csum(__wsum
hw_checksum, struct sk_buff *skb,
  }

#if IS_ENABLED(CONFIG_IPV6)

-/* In IPv6 packets, besides subtracting the pseudo header checksum,
- * we also compute/add the IP header checksum which
- * is not added by the HW.
+/* In IPv6 packets, hw_checksum lacks 6 bytes from IPv6 header:
+ * 4 first bytes : priority, version, flow_lbl
+ * and 2 additional bytes : nexthdr, hop_limit.
   */
  static int get_fixed_ipv6_csum(__wsum hw_checksum, struct sk_buff
*skb,
                               struct ipv6hdr *ipv6h)
  {
        __u8 nexthdr = ipv6h->nexthdr;
-       __wsum csum_pseudo_hdr = 0;
+       __wsum temp;

if (unlikely(nexthdr == IPPROTO_FRAGMENT ||

                     nexthdr == IPPROTO_HOPOPTS ||
                     nexthdr == IPPROTO_SCTP))
                return -1;
-       hw_checksum = csum_add(hw_checksum, (__force
__wsum)htons(nexthdr));

- csum_pseudo_hdr = csum_partial(&ipv6h->saddr,

-                                      sizeof(ipv6h->saddr) +
sizeof(ipv6h->daddr), 0);
-       csum_pseudo_hdr = csum_add(csum_pseudo_hdr, (__force
__wsum)ipv6h->payload_len);
-       csum_pseudo_hdr = csum_add(csum_pseudo_hdr,
-                                  (__force __wsum)htons(nexthdr));
-
-       skb->csum = csum_sub(hw_checksum, csum_pseudo_hdr);
-       skb->csum = csum_add(skb->csum, csum_partial(ipv6h,
sizeof(struct ipv6hdr), 0));
+       /* priority, version, flow_lbl */
+       temp = csum_add(hw_checksum, *(__wsum *)ipv6h);
+       /* nexthdr and hop_limit */
+       skb->csum = csum_add(temp, (__force __wsum)*(__be16
*)&ipv6h->nexthdr);
        return 0;
  }
  #endif