From owner-freebsd-arch Thu Mar 28 6:28:56 2002 Delivered-To: freebsd-arch@freebsd.org Received: from mail11.speakeasy.net (mail11.speakeasy.net [216.254.0.211]) by hub.freebsd.org (Postfix) with ESMTP id 5099C37B417 for ; Thu, 28 Mar 2002 06:28:42 -0800 (PST) Received: (qmail 11366 invoked from network); 28 Mar 2002 14:28:40 -0000 Received: from unknown (HELO server.baldwin.cx) ([216.27.160.63]) (envelope-sender ) by mail11.speakeasy.net (qmail-ldap-1.03) with DES-CBC3-SHA encrypted SMTP for ; 28 Mar 2002 14:28:40 -0000 Received: from laptop.baldwin.cx (gw1.twc.weather.com [216.133.140.1]) by server.baldwin.cx (8.11.6/8.11.6) with ESMTP id g2SETNv95729; Thu, 28 Mar 2002 09:29:23 -0500 (EST) (envelope-from jhb@FreeBSD.org) Message-ID: X-Mailer: XFMail 1.5.2 on FreeBSD X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit MIME-Version: 1.0 In-Reply-To: <20020328093345.Y17999-100000@salmon.nlsystems.com> Date: Thu, 28 Mar 2002 09:28:43 -0500 (EST) From: John Baldwin To: Doug Rabson Subject: RE: SMP safe reference counting Cc: arch@freebsd.org, Julian Elischer Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On 28-Mar-2002 Doug Rabson wrote: > 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. Ugh, I didn't know it was limited in what it could add. Hmmm, it would be nice to use that rather than a cmpxchg loop if possible. -- John Baldwin <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message