From owner-freebsd-questions Wed Apr 7 17:19:12 1999 Delivered-To: freebsd-questions@freebsd.org Received: from finch-post-11.mail.demon.net (finch-post-11.mail.demon.net [194.217.242.39]) by hub.freebsd.org (Postfix) with ESMTP id 04A3E14F28 for ; Wed, 7 Apr 1999 17:19:06 -0700 (PDT) (envelope-from marko@uk.radan.com) Received: from [158.152.75.22] (helo=uk.radan.com) by finch-post-11.mail.demon.net with smtp (Exim 2.12 #1) id 10V2VD-000ICt-0B; Thu, 8 Apr 1999 00:17:04 +0000 Organisation: Radan Computational Ltd., Bath, UK. Phone: +44-1225-320320 Fax: +44-1225-320311 Received: from marder-1. (rasnt-1 [193.114.228.211]) by uk.radan.com (8.6.10/8.6.10) with ESMTP id BAA00578; Thu, 8 Apr 1999 01:16:33 +0100 Received: (from marko@localhost) by marder-1. (8.9.2/8.8.8) id BAA03373; Thu, 8 Apr 1999 01:13:39 +0100 (BST) (envelope-from marko) Date: Thu, 8 Apr 1999 01:13:39 +0100 From: Mark Ovens To: Greg Lehey Cc: Darren Pilgrim , "Dragon Knight ][" , FreeBSD Questions Subject: Re: K6-2/333, was: Re: Debug kernel by default (was: System sizewith -g) Message-ID: <19990408011339.B2997@marder-1.localhost> References: <3709569A.70EEC38A@uswest.net> <37097B00.2186EB92@dtgnet.com> <3709EDEB.BE17A2E8@uswest.net> <19990407025433.C4453@marder-1.localhost> <19990407114602.Z2142@lemis.com> <19990407040113.F4453@marder-1.localhost> <19990407143044.E2142@lemis.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.95.3i In-Reply-To: <19990407143044.E2142@lemis.com>; from Greg Lehey on Wed, Apr 07, 1999 at 02:30:44PM +0930 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Wed, Apr 07, 1999 at 02:30:44PM +0930, Greg Lehey wrote: > On Wednesday, 7 April 1999 at 4:01:13 +0100, Mark Ovens wrote: > > On Wed, Apr 07, 1999 at 11:46:02AM +0930, Greg Lehey wrote: > >> On Wednesday, 7 April 1999 at 2:54:33 +0100, Mark Ovens wrote: > >>> > >>> As the person who effectively started all this discussion about > >>> bus speeds and multipliers I just want to thank all the contributors > >>> to this thread. I now have a better understanding of how it all > >>> works. The fundamental misunderstanding I had was that the CPU > >>> itself did the mutliplication and that the m/b jumpers simply "told" > >>> the CPU what multiple of the bus speed to use. > >> > >> It does. But there are various parts of the CPU. The part which > >> creates the CPU internal clock is just a bit of relatively simple > >> hardwired logic. > > > > Just when you thought it was all over.....:-) > > > > So my understanding was correct. > > Partially. > > > Other posters have suggested that the m/b supplies the multiplied > > clock frequency to the CPU and therefore the it *can't* ignore it. > > No, the MB supplies inputs to the three pins BF0, BF1 and BF2. Logic > on the CPU chip uses these inputs to multiply the incoming clock > frequency by between 2 and 5.5 in increments of 0.5 (that's 8 > different values). The rest of the CPU is blissfully unaware of > what's going on, and only looks at the clock frequency it's given. > > > However, whilst 95MHx & 3.5X is equivalent to 66MHz & 5X, if the CPU > > doesn't understand "run at 5X" then it may be running at an > > arbitrary speed (3.5X bus?). > > That depends on the CPU. Some CPUs don't sample BF2, so setting 5.0 > (which sets BF2 to 0) has the same effect as if it were high: it runs > at 3x instead of 5x. > Ah, thats what I needed to know. So as long as the CPU samples BF2 then 66MHz & 5X will have the same effect as 95MHz & 3.5X (apart from a slightly reduced CPU <==> memory speed. Thank you for the explanation. > > This all started when you said that you had noticed no (significant) > > performance increase from a K6/233 to a K6-2/333. Whilst I'm not > > disputing with you that an old HD will adversely affect performance > > on disk I/O intensive work such as compiling I would expect a > > noticeable performance increase overall, especially with 160MB of > > RAM. > > That depends on what you're doing. > > > This is what prompted me to ask if, whilst mathematically > > equivalent, 95MHz & 3.5X was the same as 66MHz & 5X in practice and > > if it isn't then that could explain the lack of performance gain. > > I understand. No, you won't get as much performance with 66x5 as you > will with 95x3.5. But my memory won't run at 95 MHz, and what we're > really comparing is the 66x5 on a K6-2 and the 66x3.5 on the K6. > Clearly the memory bandwidth doesn't change there. > > Greg > -- > See complete headers for address, home page and phone numbers > finger grog@lemis.com for PGP public key > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-questions" in the body of the message > -- FreeBSD - The Power To Serve http://www.freebsd.org My Webpage http://www.users.globalnet.co.uk/~markov _______________________________________________________________ Mark Ovens, CNC Apps Engineer, Radan Computational Ltd. Bath UK CAD/CAM solutions for Sheetmetal Working Industry mailto:marko@uk.radan.com http://www.radan.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message