linux-kernel - Re: Userspace RCU 0.2.3

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Date:	Wed, 14 Oct 2009 21:34:02 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Jon Bernard <jbernard@...ian.org>,
	Jan Blunck <jblunck@...e.de>,
	Pierre Habouzit <madcoder@...ian.org>,
	Steven Munroe <munroesj@...ux.vnet.ibm.com>,
	Bert Wesarg <bert.wesarg@...glemail.com>,
	Pierre-Marc Fournier <pierre-marc.fournier@...ymtl.ca>,
	ltt-dev@...ts.casi.polymtl.ca, rp@...s.cs.pdx.edu,
	linux-kernel@...r.kernel.org
Subject: Re: Userspace RCU 0.2.3

On Wed, Oct 14, 2009 at 10:39:25PM -0400, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> > On Wed, Oct 14, 2009 at 06:36:57PM -0400, Mathieu Desnoyers wrote:
> > > Hi,
> > > 
> > > I just released lib urcu 0.2.3, which is now using autotools. I also
> > > integrated automatic architecture detection for old 386 which lack
> > > cmpxchg (using a fall-back if necessary). I also use a lock; addl
> > > instead of mfence on x86-32 to support a larger variety of older Intel
> > > CPUs.
> > 
> > !!!
> > 
> > Is there anyone on these lists other than me who has actually used an
> > SMP 80386-based system?
> 
> SMP 386, ugh, no. But UP 386 yes (at least me). :)
> 
> It will become important as the library gets integrated in
> distributions.
> 
> > Either way, much appreciated for old time's sake.  The things we used
> > to do to avoid the need for cmpxchg!  ;-)
> 
> In this case I disable signals and take a mutex around the cmpxchg. It's
> really a best effort. Should be fine on UP 386, but not so much on SMP
> 386, as mixing it with assign/xchg pointer could lead to races. I'm not
> sure it's worth trying to support 386 SMP though.

Definitely not worth much, if anything, to support 386 SMP.

							Thanx, Paul
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