netdev - Re: [rfc] IPVS: convert scheduler management to RCU

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Date:	Fri, 20 Aug 2010 16:05:50 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Simon Horman <horms@...ge.net.au>, lvs-devel@...r.kernel.org,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	Stephen Hemminger <shemminger@...tta.com>,
	Wensong Zhang <wensong@...ux-vs.org>,
	Julian Anastasov <ja@....bg>,
	Paul E McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [rfc] IPVS: convert scheduler management to RCU

Le vendredi 20 août 2010 à 21:44 +0800, Changli Gao a écrit :
> On Fri, Aug 20, 2010 at 9:33 PM, Simon Horman <horms@...ge.net.au> wrote:
> > Signed-off-by: Simon Horman <horms@...ge.net.au>
> >
> > ---
> >
> > I'm still getting my head around RCU, so review would be greatly appreciated.
> >
> > It occurs to me that this code is not performance critical, so
> > perhaps simply replacing the rwlock with a spinlock would be better?
> >
> > Index: nf-next-2.6/net/netfilter/ipvs/ip_vs_sched.c


> > -       write_unlock_bh(&__ip_vs_sched_lock);
> > +       list_del_rcu(&scheduler->n_list);
> > +       spin_unlock_bh(&ip_vs_sched_mutex);
> 
> Need a rcu_barrier_bh().
> 
> >
> >        /* decrease the module use count */
> >        ip_vs_use_count_dec();


Quite frankly, if this is not performance critical, just use the
spinlock (and dont use 'mutex' in its name ;) )

Using RCU here will force at least one RCU grace period at dismantle
time...



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