netdev - Re: [PATCH RFC net-next] net/fib: Poptrie based FIB lookup

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Date:   Mon, 27 Aug 2018 10:56:05 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        "Md. Islam" <mislam4@...t.edu>
Cc:     Netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        makita.toshiaki@....ntt.co.jp, panda@...go.wide.ad.jp,
        yasuhiro.ohara@....com, john.fastabend@...il.com,
        alexei.starovoitov@...il.com
Subject: Re: [PATCH RFC net-next] net/fib: Poptrie based FIB lookup

On 8/27/18 10:24 AM, Stephen Hemminger wrote:
> 
> Also, as Dave mentioned any implementation needs to handle multiple namespaces
> and routing tables.
> 
> Could this alternative lookup be enabled via sysctl at runtime rather than kernel config?
> 

I spent time a couple of years ago refactoring IPv4 fib lookups with the
intent of allowing different algorithms - for use cases like this:

https://github.com/dsahern/linux/commits/net/ipv4-fib-ops

(it is also another way to solve the API nightmare that ipv6 has become).

But the poptrie patches that have been sent so far have much bigger
problems that need to be addressed before anyone worries about how to
select poptrie vs lc-trie.

The patch does not handle errors (e.g., if attributes such as tos,
metric/priority and multipath are not allowed you need to fail the route
insert; further, what happens if someone creates > 255 netdevices?),
last patch has both fib tables populated (a no-go), does not handle
delete or dumps. In the current form, the poptrie algorithm can not be
taken for a test drive. My suggestion to make it a compile time
selection is just so people can actually try it out using current admin
tools.