netdev - Re: [PATCH v4 net-next 0/5] net: More movement to fib_nh

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Date:   Wed, 3 Apr 2019 12:59:50 -0600
From:   David Ahern <dsahern@...il.com>
To:     Martin Lau <kafai@...com>, David Ahern <dsahern@...nel.org>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "idosch@...lanox.com" <idosch@...lanox.com>
Subject: Re: [PATCH v4 net-next 0/5] net: More movement to fib_nh_common

On 4/2/19 11:27 PM, Martin Lau wrote:
> On Tue, Apr 02, 2019 at 02:11:53PM -0700, David Ahern wrote:
>> From: David Ahern <dsahern@...il.com>
>>
>> Second set of three with the end goal of enabling IPv6 gateways with IPv4
>> routes.
> I am still not completely convinced on the new "*nhc" in patch 2 without
> seeing a patch showing why nh_sel is not enough.

fib_table_lookup and fib_select_path have determined the address of the
preferred fib_nh struct. To look it up again will get costly for nexthop
groups: dereference the nexthop pointer, see that it is a group, get the
pointer to the group data, find the Nth (nh_sel) entry and return it.
Since we already have the end pointer, avoid repeated lookups which
nh_sel requires and save the fib_nh to fib_result. That's what patch 2
is doing and the updated commit message shows that.