Re: [PATCH net-next 4/4] ipv6: Add support for non-equal-cost multipath

[David Ahern <dsahern@gmail.com>]

On 1/9/18 7:40 AM, Ido Schimmel wrote:
> The use of hash-threshold instead of modulo-N makes it trivial to add
> support for non-equal-cost multipath.
> 
> Instead of dividing the multipath hash function's output space equally
> between the nexthops, each nexthop is assigned a region size which is
> proportional to its weight.
> 
> Signed-off-by: Ido Schimmel <idosch@mellanox.com>
> ---
>  include/net/ip6_fib.h |  1 +
>  net/ipv6/route.c      | 11 +++++++----
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
> index 97cd05d87780..34ec321d6a03 100644
> --- a/include/net/ip6_fib.h
> +++ b/include/net/ip6_fib.h
> @@ -171,6 +171,7 @@ struct rt6_info {
>  	u32				rt6i_metric;
>  	u32				rt6i_pmtu;
>  	/* more non-fragment space at head required */
> +	int				rt6i_nh_weight;
>  	unsigned short			rt6i_nfheader_len;
>  	u8				rt6i_protocol;
>  	u8				exception_bucket_flushed:1,

Since dst is cacheline aligned there is a hole after rt6i_nh_flags. In
patch 1 you put rt6i_nh_upper_bound in that hole. Putting the weight
there too keeps those variables together as well as using the open space.