netdev - Re: [RFC PATCH 04/13] nexthop: Add implementation of resilient next-hop groups

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Message-ID: <b9a8fc9e-4e0c-7e7c-0b8a-da520c9dd837@gmail.com>
Date:   Sat, 13 Feb 2021 12:38:47 -0700
From:   David Ahern <dsahern@...il.com>
To:     Petr Machata <petrm@...dia.com>, netdev@...r.kernel.org
Cc:     David Ahern <dsahern@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [RFC PATCH 04/13] nexthop: Add implementation of resilient
 next-hop groups

On 2/8/21 1:42 PM, Petr Machata wrote:
> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> index 5d560d381070..4ce282b0a65f 100644
> --- a/net/ipv4/nexthop.c
> +++ b/net/ipv4/nexthop.c> @@ -734,6 +834,22 @@ static struct nexthop
*nexthop_select_path_mp(struct nh_group *nhg, int hash)
>  	return rc;
>  }
>  
> +static struct nexthop *nexthop_select_path_res(struct nh_group *nhg, int hash)
> +{
> +	struct nh_res_table *res_table = rcu_dereference(nhg->res_table);
> +	u32 bucket_index = hash % res_table->num_nh_buckets;

Have you considered requiring the number of buckets to be a power of 2
to avoid the modulo in the hot path? Seems like those are the more
likely size options.