netdev - Re: [RFC] netfilter: get rid of atomic ops in fast path

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Date:	Wed, 16 Mar 2011 13:16:48 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	kaber@...sh.net, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org, hawk@...u.dk
Subject: Re: [RFC] netfilter: get rid of atomic ops in fast path

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 16 Mar 2011 20:00:05 +0100

> We currently use a percpu spinlock to 'protect' rule bytes/packets
> counters, after various attempts to use RCU instead.
> 
> Lately we added a seqlock so that get_counters() can run without
> blocking BH or 'writers'. But we really use the seqcount in it.
> 
> Spinlock itself is only locked by the current cpu, so we can remove it
> completely.
> 
> This cleanups api, using correct 'writer' vs 'reader' semantic.
> 
> At replace time, the get_counters() call makes sure all cpus are done
> using the old table.
> 
> We could probably avoid blocking BH (we currently block them in xmit
> path), but thats a different topic ;)
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

FWIW, I think this is a great idea.
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