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

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Message-Id: <1240904468.7620.70.camel@twins>
Date:	Tue, 28 Apr 2009 09:41:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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>, paulmck@...ux.vnet.ibm.com,
	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 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.

> That also probably clarifies the rules on when you use one over the other 
> (ie reading off all the statistics is a "global" operation, as is 
> obviously replacing the tables).
> 
> Of course, "readers" and "writers" is something most Linux lock people are 
> more used to. Or "brlock" for the old-timers, but that involves a heavy 
> dose of bad taste. The new use is much nicer, especially since it never 
> takes the global lock on _all_ cpu's (which was really a killer in so 
> many ways).
> 
> 			Linus
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