From owner-freebsd-smp Sat Dec 9 17:16:52 2000 From owner-freebsd-smp@FreeBSD.ORG Sat Dec 9 17:16:50 2000 Return-Path: Delivered-To: freebsd-smp@freebsd.org Received: from sharmas.dhs.org (c62443-a.frmt1.sfba.home.com [24.0.69.165]) by hub.freebsd.org (Postfix) with ESMTP id 33A3E37B400 for ; Sat, 9 Dec 2000 17:16:50 -0800 (PST) Received: from sharmas.dhs.org ([192.168.1.17]) by sharmas.dhs.org (8.9.3/8.9.3) with ESMTP id RAA29155; Sat, 9 Dec 2000 17:15:08 -0800 Message-ID: <3A318757.4040108@sharmas.dhs.org> Date: Fri, 08 Dec 2000 17:13:59 -0800 From: Arun Sharma User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; m18) Gecko/20001121 X-Accept-Language: en MIME-Version: 1.0 To: Chuck Paterson Cc: smp@FreeBSD.ORG Subject: Re: Userland atomic assignments References: <200012091602.eB9G2UH06249@berserker.bsdi.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-freebsd-smp@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Chuck Paterson wrote: > } > }However, the complexity comes from memory ordering issues. All of x86 boxes > }ensure sequential consistency. > } > > Sequenctial consistency from a single processor, which may well > be what you meant. Actually, what I wrote in my previous mail wasn't completely accurate about sequential consistency. (c == d) => (a == b) basically means writes happen in program order as you say above. > Writes from different processors to different cache lines are not > ordered with respect to one another. Also writes from one processor > are not at all ordered with respect to reads from another processor. > > What is guaranteed is that writes from a single processor will be > ordered with respect to one another as viewed from any processor. What sequential consistency guarantees is that writes as seen from some other processor would make sense for _some_ arbitrary intermixing of writes from other processors. A more formal definition: http://whatis.techtarget.com/WhatIs_Definition_Page/0,4152,212962,00.html -Arun To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message