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

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Date:	Fri, 20 Aug 2010 10:16:23 -0400
From:	yao zhao <dragonlinux@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>, 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

On Fri, Aug 20, 2010 at 10:05 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 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 ;) )
>
if it is not performance critical, you should use  the
read_lock/write_lock, it should make the readers happier than
spinlock. the name "mutex" is a little bit confuse.
synchronize_rcu() is not necessary when you only need to delete from a
list as it is atomic.

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