netdev - Re: [PATCH net-next 06/12] ipvs: optimize dst usage for real server

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Message-Id: <20130306.151810.1494132480233578627.davem@davemloft.net>
Date:	Wed, 06 Mar 2013 15:18:10 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ja@....bg
Cc:	horms@...ge.net.au, lvs-devel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 06/12] ipvs: optimize dst usage for real server

From: Julian Anastasov <ja@....bg>
Date: Wed,  6 Mar 2013 10:42:16 +0200

> 	Currently when forwarding requests to real servers
> we use dst_lock and atomic operations when cloning the
> dst_cache value. As the dst_cache value does not change
> most of the time it is better to use RCU and to lock
> dst_lock only when we need to replace the obsoleted dst.
> For this to work we keep dst_cache in new structure protected
> by RCU. For packets to remote real servers we will use noref
> version of dst_cache, it will be valid while we are in RCU
> read-side critical section because now dst_release for replaced
> dsts will be invoked after the grace period. NAT-ed packets
> via loopback that are not sent but are passed to local stack
> with NF_ACCEPT need a dst clone (skb_dst_force).
> 
> Signed-off-by: Julian Anastasov <ja@....bg>

It think it's much cleaner to have the callers of route lookups do
skb_set_dst_noref().

Then you don't need any new interfaces, and you therefore don't need
to expose bits of the noref implementation and semantics at all.
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