Author: enrico carrisco
Date: 03:47:48 02/21/03
Go up one level in this thread
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.
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