netdev - Re: state of rtcache removal...

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Message-Id: <20110216.223932.112610567.davem@davemloft.net>
Date:	Wed, 16 Feb 2011 22:39:32 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: state of rtcache removal...

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 17 Feb 2011 07:25:15 +0100

> Thanks David for this work in progress.

It was my pleasure :-)

> If I remember my works in last October/November, I also know fib_hash
> was a bit faster than fib_trie (around 20%)...

Right, if table is small hash can be faster.

I just wrote a hack that puts fib_lookup() results into the the
flow cache, and hooked it only into the one fib_lookup() call
that happens in ip_route_output_slow().

This pointed out another costly thing we do when resolving output
routes.  If the flow key's source is not INADDR_ANY, we validate the
source address is our's by doing a fib table lookup in the local
table, with the address in the flow key's destination field.

So even on output we were doing 3 fib lookups :-/

Therefore, the flow cache hack gets rid of 2 of those 3.
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