netdev - Re: [PATCH 00/16] Remove the ipv4 routing cache

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Message-Id: <20120726.200846.66786272076299783.davem@davemloft.net>
Date:	Thu, 26 Jul 2012 20:08:46 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	alexander.duyck@...il.com
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH 00/16] Remove the ipv4 routing cache

From: Alexander Duyck <alexander.duyck@...il.com>
Date: Thu, 26 Jul 2012 19:14:55 -0700

> Any idea why these look-ups are so expensive in the first place?  When
> I dump fib_trie it doesn't look like I have much there.  I would have
> thought the table would be pretty static with just 8 flows all going
> to the same destination address, but it seems like I was getting hit
> with cache misses for some reason.

A lot of the overhead comes from write traffic that results from
filling in the "fib_result" structure onto the callers stack.

The return value from a fib_lookup() has far too many components.  But
simplifying things is not easy.
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