Author: Aaron Gordon
Date: 12:00:17 02/21/03
Go up one level in this thread
On February 21, 2003 at 09:55:56, Robert Hyatt wrote: >On February 21, 2003 at 06:47:48, enrico carrisco wrote: > >>On February 20, 2003 at 11:55:42, Robert Hyatt wrote: >> >>>On February 20, 2003 at 09:36:24, Jeremiah Penery wrote: >>> >>>>Prime95 is a real-world application. It does very intense mathematical >>>>calculation, testing several-million-digit numbers for primality. I don't >>>>believe there's another program that will detect CPU problems faster. >>>> >>> >>>The problem is that it won't detect _any_ floating point problems. Nor problems >>>with unlikely instructions such as BSF/BSR, or fiddling with O/S issues like >>>cache flushing, fiddling with the memory type and range registers, and so forth. >>> >>>There is a _lot_ of the chip that such an application simply doesn't touch, and >>>when >>>you use such a test to say "it works" it is like flipping a coin. If all you do >>>is use >>>the same instructions, you may well have a winner. But if you use something >>>that your >>>test didn't exercise, who knows? >>> >>>I don't have time for those kinds of random problems. If you do, that's >>>certainly up >>>to you to choose overclocking. >>> >>> >>>>I overclocked my CPU for a while, and it appeared to be completely stable. I >>>>could run Crafty for days with no problems, and I never had a crash or bug in >>>>any other application. I ran Prime95 for a while, where a calculation error was >>>>soon detected. Of course, when I clocked back to the normal level, the error >>>>went away. >>> >>>Unfortunately your testing is backward. You assumed it was good because it ran >>>without "crashing". But are you _sure_ crafty never computed a bad score? Or >>>hosed >>>the hash signature? Or generated a bogus move? No way to know. And if prime95 >>>runs with no errors, are you _sure_ all the floating point stuff works? MMX >>>stuff >>>works? Oddball things like bsf/bsr? >>> >>>That's the flaw in this... >>> >>> >>> >>> >>> >>> >>>> >>>>I was running at somewhere near the maximum rated speed for that particular >>>>core, which had about zero headroom to begin with, so the errors weren't all >>>>that surprising to me. Had I bought a slower chip, I could have overclocked it >>>>to the speed of my current chip very safely, as the core obviously has the >>>>ability to run at that speed. Overclocking becomes particularly unsafe when one >>>>tries to run at a speed above the normal ability of the core. Otherwise, it's >>>>not much more than what the manufacturers do by taking chips from the same >>>>silicon wafer and splitting them into different CPU speed bins, as those chips >>>>should be theoretically _identical_. >>> >>>Note that we are not talking about buying 2.0ghz xeons and overclocking to 2.4. >>>We are >>>talking about buying the fastest chips made and overclocking _those_. That is a >>>completely >>>different issue, and that is what is being done in the cases being discussed... >> >>How do you know what the maximum _planned_ speed of a certain core is? Until >>you know that, the whole discussion is an endless loop. >> >>-elc. > > >When I did TTL design years ago, I simply took the published gate delays for >every circuit I used. NAND gates, NOR gates, 16-1 mux, 1-16 demux, an ALU, >you name it. I added up the gate delays, plus the published tolerances, and >started testing somewhere longer than that and shortened the clock to the >actual number computed by the longest-path analysis. > >The engineers _know_ what the max speed is. I hope you don't think they lay >the thing out, build it, then see how fast it will run? Sure they do, up to a point. AMD knows they'll be hitting ~2.3GHz minimum so it's "safe" to make 2.25GHz 2800+ chips. Some do more, but the least you can expect even with a really bad cooler and crappy motherboard is ~2.3GHz. That was my point earlier in the overclocking discussion. You *CAN* hit 2.3GHz reliably, any more and you'll need to test it because you'd be pushing your luck. Same goes with the P4. They're producing at least 3.2GHz silicon.
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