Date: Fri, 08 Dec 2000 17:13:59 -0800 From: Arun Sharma <arun@sharmas.dhs.org> To: Chuck Paterson <cp@bsdi.com> Cc: smp@FreeBSD.ORG Subject: Re: Userland atomic assignments Message-ID: <3A318757.4040108@sharmas.dhs.org> References: <200012091602.eB9G2UH06249@berserker.bsdi.com>
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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
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