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

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Date:	Fri, 20 Aug 2010 16:32:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	yao zhao <dragonlinux@...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

Le vendredi 20 août 2010 à 10:16 -0400, yao zhao a écrit :

> 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.

Yes, I mentioned the 'mutex' name oddity.

Point is :

We want to remove read_write locks. They dont fit the bill.

If performance critical, lot of readers -> RCU (a lot faster)
If not, or too much writers versus readers -> spinlock (a bit faster)



> synchronize_rcu() is not necessary when you only need to delete from a
> list as it is atomic.
> 

Thats a rather strange and completely wrong claim. A big part of RCU job
is to have appropriate work done on deletes. Inserts are more easy (only
needs a smp_wmb())

Take a look at Documentation/RCU/* before saying such things ;)

Not only synchronize_rcu() is not enough to protect this kind of code,
but you need something stronger.


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