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Message-ID: <AANLkTiksJuR3vzK2SgfT3BnwddMbTq3SX3ae2PMKXd0O@mail.gmail.com>
Date: Fri, 28 May 2010 11:43:31 +0530
From: ratheesh k <ratheesh.ksz@...il.com>
To: Stephen Hemminger <shemminger@...tta.com>
Cc: netdev@...r.kernel.org, linux-net@...r.kernel.org
Subject: Re: fn_trie_lookup and fn_hash_lookup
On Fri, May 28, 2010 at 9:10 AM, Stephen Hemminger
<shemminger@...tta.com> wrote:
> On Fri, 28 May 2010 08:53:11 +0530
> ratheesh k <ratheesh.ksz@...il.com> wrote:
>
>> hi ,
>>
>> I was looking into 2.6.18 kernel . I can see two functions
>> fn_trie_lookup , fn_hash_lookup
>>
>> ipv4/fib_trie.c: tb->tb_lookup = fn_trie_lookup;
>> ipv4/fib_hash.c: tb->tb_lookup = fn_hash_lookup;
>>
>> What is the differnce between these two functions ?
>
> They are the two possible FIB algorithms configurable.
>
> net/ipv4/Kconfig:
>
> choice
> prompt "Choose IP: FIB lookup algorithm (choose FIB_HASH if unsure)"
> depends on IP_ADVANCED_ROUTER
> default ASK_IP_FIB_HASH
>
> config ASK_IP_FIB_HASH
> bool "FIB_HASH"
> ---help---
> Current FIB is very proven and good enough for most users.
>
> config IP_FIB_TRIE
> bool "FIB_TRIE"
> ---help---
> Use new experimental LC-trie as FIB lookup algorithm.
> This improves lookup performance if you have a large
> number of routes.
>
> LC-trie is a longest matching prefix lookup algorithm which
> performs better than FIB_HASH for large routing tables.
> But, it consumes more memory and is more complex.
>
> LC-trie is described in:
>
> IP-address lookup using LC-tries. Stefan Nilsson and Gunnar Karlsson
> IEEE Journal on Selected Areas in Communications, 17(6):1083-1092,
> June 1999
>
> An experimental study of compression methods for dynamic tries
> Stefan Nilsson and Matti Tikkanen. Algorithmica, 33(1):19-33, 2002.
> http://www.nada.kth.se/~snilsson/public/papers/dyntrie2/
>
>
> Also see Documentation/networking/fib_trie.txt
>
>
>
Thanks ..
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