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

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Date:	Thu, 26 Jul 2012 19:14:55 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH 00/16] Remove the ipv4 routing cache

On Thu, Jul 26, 2012 at 3:53 PM, David Miller <davem@...emloft.net> wrote:
> From: Alexander Duyck <alexander.duyck@...il.com>
> Date: Thu, 26 Jul 2012 15:03:39 -0700
>
>> Here is the latest perf results with all of these patches in place.
>> As you predicted your patch essentially cut the lookup overhead in
>> half:
>
> Ok good.
>
> That patch is hard to make legitimate, I'd have to do a bit or work
> before we could realize that change.
>
> We can only combine the LOCAL and MAIN tables like that so long as
> there are no overlaps in the routes covered by the two tables.  We'd
> also have to be sure to report the routes properly in dumps too.
>
> I really wish we had never segregated these two tables, it's
> completely pointless and hurts performance.  But now we have to
> accomodate this legacy.

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.

Thanks,

Alex
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