netdev - Re: [PATCH] ipv4: Remove fib

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Date:	Wed, 2 Feb 2011 08:29:21 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: Remove fib_hash.

On Tue, 01 Feb 2011 18:15:42 -0800 (PST)
David Miller <davem@...emloft.net> wrote:

> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 02 Feb 2011 01:48:13 +0100
> 
> > Hmm... I know having to maintain two implementations is time consuming,
> > but I know fib_trie is bigger :
> > 
> > # size net/ipv4/fib_*.o
> >    text	   data	    bss	    dec	    hex	filename
> >    7252	    120	      0	   7372	   1ccc	net/ipv4/fib_frontend.o
> >    7279	     16	      4	   7299	   1c83	net/ipv4/fib_hash.o
> >    1479	      0	      0	   1479	    5c7	net/ipv4/fib_rules.o
> >    7885	      0	   2080	   9965	   26ed	net/ipv4/fib_semantics.o
> >   16222	     16	     16	  16254	   3f7e	net/ipv4/fib_trie.o
> > 
> > In my tests, I know that fib_trie is more expensive for typical routing
> > tables for hosts (no more than a dozen or entries), in latencies
> > results, mostly because of icache misses, but also dcache ones.
> 
> It's mostly the rebalancing code that takes up the space.
> 
> The lookup path is on the same order of magnitude as the fib hash
> stuff was.
> 
> In any event, we have several months to hash out any regressions and I
> think if I didn't do this removal nobody would work on it so... :-)

For the case of small devices, what about keeping fib_hash as option
under CONFIG_EMBEDDED. And remove all the magic resizing of hash table.
Get back to something with really small size.

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