Author: Robert Hyatt
Date: 16:34:08 02/21/03
Go up one level in this thread
On February 21, 2003 at 15:00:17, Aaron Gordon wrote: >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. I have said it many times. If you believe that, feel free to continue to push the envelope. You _will_ get bit at some point in time. Hopefully not on something that causes great problems...
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