Date: Thu, 28 Mar 2002 09:36:38 +0000 (GMT) From: Doug Rabson <dfr@nlsystems.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Julian Elischer <julian@elischer.org>, <arch@freebsd.org> Subject: RE: SMP safe reference counting Message-ID: <20020328093345.Y17999-100000@salmon.nlsystems.com> In-Reply-To: <XFMail.20020327165157.jhb@FreeBSD.org>
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On Wed, 27 Mar 2002, John Baldwin wrote: > > On 27-Mar-2002 Julian Elischer wrote: > > > > [please remove -smp from your reply] > > > > Once again on the SMP list a lock is being used to make a reference count > > safe. I'd like to re-raise the issue of a safe reference counting > > fascility. > > > > what would be the semantics? > > I have refcount.patch :) What would be nice is to first implement > atomic_fetchadd() (xadd on 486+, some hack on 386, fetchadd on ia64, similar to > atomic_add on sparc64, alpha, and powerpc I believe, basically it would add a > value to a memory location and return the result). You can then use taht for > the reference_release (or whatever you call it). We could also use that to get > rid of the really bloated debug version that uses a mutex and have a much > smaller debug version that still uses atomic ops. The ia64 has a fetchadd instruction which can add a constant to memory, returning the old value. It is limited to adding only the constants -16. -8, -4, -1, 1, 4, 8, 16. -- Doug Rabson Mail: dfr@nlsystems.com Phone: +44 20 8348 6160 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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