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

[Saeed Mahameed <saeedm@mellanox.com>]

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 <edumazet@google.com>
> Cc: Saeed Mahameed <saeedm@mellanox.com>
> Cc: Tariq Toukan <tariqt@mellanox.com>
> ---
> Note: This patch, like other mlx4 patches can definitely wait
> Tariq approval, thanks !
> 

LGTM,

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

>  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