From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by oss.sgi.com (8.11.2/8.11.3) id g1180uZ25548 for linux-mips-outgoing; Fri, 1 Feb 2002 00:00:56 -0800 Received: from ocean.lucon.org (12-234-19-19.client.attbi.com [12.234.19.19]) by oss.sgi.com (8.11.2/8.11.3) with SMTP id g1180pd25544 for ; Fri, 1 Feb 2002 00:00:51 -0800 Received: by ocean.lucon.org (Postfix, from userid 1000) id 59746125C3; Thu, 31 Jan 2002 23:00:50 -0800 (PST) Date: Thu, 31 Jan 2002 23:00:50 -0800 From: "H . J . Lu" To: Hiroyuki Machida Cc: kaz@ashi.footprints.net, macro@ds2.pg.gda.pl, libc-alpha@sources.redhat.com, linux-mips@oss.sgi.com Subject: Re: [libc-alpha] Re: PATCH: Fix ll/sc for mips Message-ID: <20020131230050.C32690@lucon.org> References: <20020201.123523.50041631.machida@sm.sony.co.jp> <20020201.135903.123568420.machida@sm.sony.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20020201.135903.123568420.machida@sm.sony.co.jp>; from machida@sm.sony.co.jp on Fri, Feb 01, 2002 at 01:59:03PM +0900 Sender: owner-linux-mips@oss.sgi.com Precedence: bulk On Fri, Feb 01, 2002 at 01:59:03PM +0900, Hiroyuki Machida wrote: > > From: Kaz Kylheku > Subject: Re: [libc-alpha] Re: PATCH: Fix ll/sc for mips > Date: Thu, 31 Jan 2002 20:02:25 -0800 (PST) > > > On Fri, 1 Feb 2002, Hiroyuki Machida wrote: > > > Please note that "sc" may fail even if nobody write the > > > variable. (See P.211 "8.4.2 Load-Linked/Sotre-Conditional" of "See > > > MIPS RUN" for more detail.) > > > So, after your patch applied, compare_and_swap() may fail, even if > > > *p is equal to oldval. > > > > I can't think of anything that will break because of this, as long > > as the compare_and_swap eventually succeeds on some subsequent trial. > > If the atomic operation has to abort for some reason other than *p being > > unequal to oldval, that should be cool. > > I mean that this patch breaks the spec of compare_and_swap(). > In most case, this patch may works as Kaz said. If this patch have > no side-effect to any application, it's ok to apply the patch. But > we can't know how to use compare_and_swap() in all aplications in a > whole world. So we have to follow the spec. > Please note that the old compare_and_swap is broken. If you use compare_and_swap to check if *p == oldval, my patch doesn't help you. But if you use it to swap old/new, my patch works fine. But I don't think you can use it check if *p == oldval since *p can change at any time. It is the same as simply using "*p == oldval". I don't see my patch should break any sane applications. H.J.