netdev - Re: [RFC PATCH] netfilter: remove the duplicate tables

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Message-ID: <alpine.LNX.2.01.1011191354160.20769@obet.zrqbmnf.qr>
Date:	Fri, 19 Nov 2010 13:57:22 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Changli Gao <xiaosuo@...il.com>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [RFC PATCH] netfilter: remove the duplicate tables

On Friday 2010-11-19 13:48, Changli Gao wrote:

>On Fri, Nov 19, 2010 at 7:29 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>> IMHO, the real problem is not the table duplication. We know that adding
>> a level of indirection is going to hurt a lot because of cache misses.
>>
>
>Currently, multi-core CPU is common, the cores in a CPU share the
>lowest level cache. Duplicate tables use more RAM, and may cause more
>pressure of the lowest level cache.

There probably should be at most one copy per NUMA node. Maybe less, 
depending on what the benchmarks will say.

I started on some patch to reduce the ruleset from #cpu to #numa_nodes, 
but then stopped when I ran into the obvious fact that it would require 
locking the counters because xtables can actually run on more than one 
core within a given numa node. When decoupling counters from the 
ruleset, reducing the ruleset copies would become easier.
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