linux-kernel - Re: [rp] Userspace RCU 0.2.3

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Message-ID: <20091018225234.GA9164@elf.ucw.cz>
Date:	Mon, 19 Oct 2009 00:52:35 +0200
From:	Pavel Machek <pavel@....cz>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Pierre-Marc Fournier <pierre-marc.fournier@...ymtl.ca>,
	Jan Blunck <jblunck@...e.de>,
	Steven Munroe <munroesj@...ux.vnet.ibm.com>,
	rp@...s.cs.pdx.edu, Josh Triplett <josh@...htriplett.org>,
	linux-kernel@...r.kernel.org, ltt-dev@...ts.casi.polymtl.ca,
	Pierre Habouzit <madcoder@...ian.org>,
	Jon Bernard <jbernard@...ian.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Bert Wesarg <bert.wesarg@...glemail.com>
Subject: Re: [rp] Userspace RCU 0.2.3

On Sun 2009-10-18 18:02:43, Mathieu Desnoyers wrote:
> * Pavel Machek (pavel@....cz) wrote:
> > On Thu 2009-10-15 13:40:54, Pierre-Marc Fournier wrote:
> > > Josh Triplett wrote:
> > > > 
> > > > Even Debian has given up on real 386 systems at this point, primarily
> > > > because system libraries like glibc have; 486 and better represents the
> > > > bare minimum required at this point.  I don't know of any distributions
> > > > supporting real 386 systems at this point, and doing so would represent
> > > > a major undertaking.
> > > > 
> > > 
> > > What about embedded systems? Anyone know if some 386 chips, perhaps even
> > > in smp configurations, are still in use in those?
> > 
> > smp 386: definitely not.
> 
> Hrm, so for UP 386, I wonder what's the best approach.
> 
> One would be to encapsulate all write accesses to the RCU pointers. If
> we detect that the architecture lacks cmpxchg, _all_ update operations
> (rcu_assign_pointer, rcu_xchg_pointer and rcu_cmpxchg_pointer) would
> have to use the signal-disabled+mutex fall-back.
> 
> Does it make sense ?

Yep, but it sounds expensive. Another option is to ignore the issue
and see how many people still have 386s :-). Few  embedded  systems
may be affected, but...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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