netdev - Re: [PATCH] netfilter: use per-CPU r**ursive lock {XV}

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Date:	Tue, 28 Apr 2009 07:22:59 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	Ingo Molnar <mingo@...e.hu>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Eric Dumazet <dada1@...mosbay.com>,
	David Miller <davem@...emloft.net>,
	Jarek Poplawski <jarkao2@...il.com>,
	Paul Mackerras <paulus@...ba.org>, kaber@...sh.net,
	jeff.chua.linux@...il.com, laijs@...fujitsu.com,
	jengelh@...ozas.de, r000n@...0n.net, linux-kernel@...r.kernel.org,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	benh@...nel.crashing.org
Subject: Re: [PATCH] netfilter: use per-CPU r**ursive lock {XV}

On Tue, Apr 28, 2009 at 09:41:08AM +0200, Peter Zijlstra wrote:
> On Mon, 2009-04-27 at 16:32 -0700, Linus Torvalds wrote:
> > 
> > On Mon, 27 Apr 2009, Linus Torvalds wrote:
> > > 
> > > I left the commentary about "readers" and "writers", because in many
> > > ways it's correct, and what the code actually does is very much to
> > > emulate a reader-writer lock.  I put quotes around the uses in the
> > > comments to high-light that it largely _acts_ as a reader-writer lock. 
> > 
> > Btw, I think it was Paul who pointed out that technically it's probably 
> > better to call them "local" and "global" lockers instead of "readers" and 
> > "writers".
> 
> exclusive vs non-exclusive is what the literature would call them in
> most cases I think.

I would argue that the non-exclusive category includes both reader-writer
locking and local-global locking.  That said, we have an unusual variant
of local-global in this case, as the global processing acquires only one
of the locks at a time.

							Thanx, Paul
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