netdev - Re: [PATCH nf-next-2.6 2/2] conntrack: per

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Message-ID: <1276008733.2486.177.camel@edumazet-laptop>
Date:	Tue, 08 Jun 2010 16:52:13 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Changli Gao <xiaosuo@...il.com>,
	Netfilter Developers <netfilter-devel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH nf-next-2.6 2/2] conntrack: per_cpu untracking

Le mardi 08 juin 2010 à 16:29 +0200, Patrick McHardy a écrit :
> On 04.06.2010 22:15, Eric Dumazet wrote:
> > NOTRACK makes all cpus share a cache line on nf_conntrack_untracked
> > twice per packet, slowing down performance.
> > 
> > This patch converts it to a per_cpu variable.
> > 
> > We assume same cpu is used for a given packet, entering and exiting the
> > NOTRACK state.
> 
> That doesn't seem to be a valid assumption, the conntrack entry is
> attached to the skb and processing in the output path might get
> preempted and rescheduled to a different CPU.

Thats unfortunate.

Ok, only choice then is to not change refcount on the untracked ct, and
keep a shared (read only after setup time) untrack structure.





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