Date: Thu, 18 Jan 2001 07:06:09 +1100 From: Peter Jeremy <peter.jeremy@alcatel.com.au> To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> Cc: current@FreeBSD.ORG Subject: Re: Atomic breakage? Message-ID: <20010118070608.D98607@gsmx07.alcatel.com.au> In-Reply-To: <200101171543.KAA18055@khavrinen.lcs.mit.edu>; from wollman@khavrinen.lcs.mit.edu on Wed, Jan 17, 2001 at 10:43:10AM -0500 References: <3A64AA23.30035A1C@elischer.org> <Pine.BSF.4.21.0101171400210.3074-100000@besplex.bde.org> <20010116191009.E7240@fw.wintelcom.net> <20010117142654.A98607@gsmx07.alcatel.com.au> <200101171543.KAA18055@khavrinen.lcs.mit.edu>
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On 2001-Jan-17 10:43:10 -0500, Garrett Wollman <wollman@khavrinen.lcs.mit.edu> wrote: ><<On Wed, 17 Jan 2001 14:26:54 +1100, Peter Jeremy <peter.jeremy@alcatel.com.au> said: > >> To support multiple masters, you need proper locks. > >On older processors, yes. On processors with the CX8 feature bit set, >you can do it without any sort of locking (indeed, this is a primitive >that semaphores can be built upon). This particular sub-thread was specifically discussing the 80386 - as I thought was clear from the context. I am aware of the CMPXCHG8B insn, but it's not relevant to the 386 or 486. >On pre-Pentium processors (which lack the CX8 feature) this sort of >sequence is impossible. OTOH, I don't think SMP works on any >pre-Pentium processor, so again this degenerates to: There are SMP machines using both 386 and 486 processors. There is no support in FreeBSD for SMP on pre-Pentium processors. Peter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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