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

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Message-ID: <20091018231624.GC5946@Krystal>
Date:	Sun, 18 Oct 2009 19:16:24 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Pavel Machek <pavel@....cz>
Cc:	Pierre Habouzit <madcoder@...ian.org>,
	Steven Munroe <munroesj@...ux.vnet.ibm.com>,
	rp@...s.cs.pdx.edu, linux-kernel@...r.kernel.org,
	Josh Triplett <josh@...htriplett.org>,
	ltt-dev@...ts.casi.polymtl.ca, Jon Bernard <jbernard@...ian.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jan Blunck <jblunck@...e.de>
Subject: Re: [ltt-dev] [rp] Userspace RCU 0.2.3

* Pavel Machek (pavel@....cz) wrote:
> 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...
> 

I can keep that as a special build option, e.g.

target: i386

Mathieu

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