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

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Message-Id: <20120725.163939.581743307449189972.davem@davemloft.net>
Date:	Wed, 25 Jul 2012 16:39:39 -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: David Miller <davem@...emloft.net>
Date: Wed, 25 Jul 2012 16:17:32 -0700 (PDT)

> From: Alexander Duyck <alexander.duyck@...il.com>
> Date: Wed, 25 Jul 2012 16:02:45 -0700
> 
>> Since your patches are in I have started to re-run my tests. I am
>> seeing a significant drop in throughput with 8 flows which I expected,
>> however it looks like one of the biggest issues I am seeing is that
>> the dst_hold and dst_release calls seem to be causing some serious
>> cache thrash.  I was at 12.5Mpps w/ 8 flows before the patches, after
>> your patches it drops to 8.3Mpps.
> 
> Yes, this is something we knew would start happening.
> 
> One idea is to make cached dsts be per-cpu in the nexthops.

Actually I think what really kills your case is the removal of the
noref path for route lookups.  I'll work on a patch to restore that
in the case where we use cached routes from the FIB nexthops.
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