linux-kernel - Re: [ltt-dev] [RFC git tree] Userspace RCU (urcu) for Linux (repost)

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Message-ID: <alpine.LFD.2.00.0902121247040.3099@localhost.localdomain>
Date:	Thu, 12 Feb 2009 13:15:08 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	ltt-dev@...ts.casi.polymtl.ca, linux-kernel@...r.kernel.org,
	Bryan Wu <cooloney@...nel.org>,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [ltt-dev] [RFC git tree] Userspace RCU (urcu) for Linux
 (repost)



On Thu, 12 Feb 2009, Paul E. McKenney wrote:
> 
> In other words, you are arguing for using ACCESS_ONCE() in the loops,
> but keeping the old ACCESS_ONCE() definition, and declaring BF hardware
> broken?

Well, I _also_ argue that if you have a busy loop, you'd better have a 
cpu_relax() in there somewhere anyway. If you don't, you have a bug.

So I think the BF approach is "borderline broken", but I think it should 
work, if BF just has whatever appropriate cache flush in its cpu_relax.

			Linus
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