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Old 2013-01-28, 20:33   #1
AlTonno15
 

7×1,031 Posts
Question Strange benchmark results

Hello,

I've got a weird problem some folks in here might help me with.


I'm examining an old CPU/Mainboard-Combo - it's an Intel Core2Duo E6600 placed on an Intel DQ965GF running at default 2,4Ghz with stock cooler.
The reason I'm taking a closer look is, that the CPU got ridiculously slow with a constant high load. System age is about 6 years, and it has been in use all the time (mostly for office and browsing)


I did a clean new installation of WinXP Pro 32bit to rule out any OS impact and ran a couple of Benchmarks in Prime95.

The results always looked like this:


Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz
CPU speed: 2397.68 MHz, 2 cores
CPU features: Prefetch, SSE, SSE2
L1 cache size: 32 KB
L2 cache size: 4 MB
L1 cache line size: 64 bytes
L2 cache line size: 64 bytes
TLBS: 256
Prime95 32-bit version 27.7, RdtscTiming=1
Best time for 768K FFT length: 1511.908 ms., avg: 1552.140 ms.
Best time for 896K FFT length: 51.404 ms., avg: 55.551 ms.
Best time for 1024K FFT length: 30.168 ms., avg: 32.167 ms.
Best time for 1280K FFT length: 27.854 ms., avg: 31.321 ms.
Best time for 1536K FFT length: 3073.126 ms., avg: 3191.737 ms.
Best time for 1792K FFT length: 37.038 ms., avg: 41.056 ms.
Best time for 2048K FFT length: 4152.101 ms., avg: 4523.601 ms.
Best time for 2560K FFT length: 5253.055 ms., avg: 5572.654 ms.
Best time for 3072K FFT length: 4808.327 ms., avg: 4839.167 ms.
Best time for 3584K FFT length: 162.240 ms., avg: 177.086 ms.
Best time for 4096K FFT length: 8468.204 ms., avg: 8540.221 ms.
Best time for 5120K FFT length: 10555.163 ms., avg: 10911.235 ms.
Best time for 6144K FFT length: 13175.753 ms., avg: 13204.398 ms.
Best time for 7168K FFT length: 20337.303 ms., avg: 20608.073 ms.
Best time for 8192K FFT length: 283.167 ms., avg: 300.003 ms.

Timing FFTs using 2 threads.
Best time for 768K FFT length: 702.859 ms., avg: 734.454 ms.
Best time for 896K FFT length: 13.779 ms., avg: 15.124 ms.
Best time for 1024K FFT length: 12.861 ms., avg: 13.729 ms.
Best time for 1280K FFT length: 24.498 ms., avg: 26.125 ms.
Best time for 1536K FFT length: 1521.824 ms., avg: 1564.637 ms.
Best time for 1792K FFT length: 25.966 ms., avg: 28.135 ms.
Best time for 2048K FFT length: 2071.858 ms., avg: 2086.971 ms.
Best time for 2560K FFT length: 2565.722 ms., avg: 2605.546 ms.
Best time for 3072K FFT length: 2329.320 ms., avg: 2371.183 ms.
Best time for 3584K FFT length: 55.653 ms., avg: 58.532 ms.
Best time for 4096K FFT length: 4160.414 ms., avg: 4178.362 ms.
Best time for 5120K FFT length: 5374.089 ms., avg: 5398.690 ms.
Best time for 6144K FFT length: 6623.888 ms., avg: 6706.953 ms.
Best time for 7168K FFT length: 9891.660 ms., avg: 9930.165 ms.
Best time for 8192K FFT length: 125.284 ms., avg: 133.368 ms.
Best time for 61 bit trial factors: 4.607 ms.
Best time for 62 bit trial factors: 4.545 ms.
Best time for 63 bit trial factors: 3494.402 ms.
Best time for 64 bit trial factors: 3485.577 ms.
Best time for 65 bit trial factors: 7.258 ms.
Best time for 66 bit trial factors: 7.543 ms.
Best time for 67 bit trial factors: 7.203 ms.
Best time for 75 bit trial factors: 7.696 ms.
Best time for 76 bit trial factors: 7.677 ms.
Best time for 77 bit trial factors: 7.676 ms.


I compared these values to the ones here http://www.mersenne.ca/bench.php?cpu...00+%40+2.40GHz
Obviously, there are two types of results: for some FFT lengths they seem to be fine, but for others the times really stand out (up to 20 seconds!)
The "affected" FFT values were the same in every benchmark run.


I can imagine that a CPU may wear out over time, but (as far as I know) this one has never been overclocked or used for excessive gaming and should imho still be fine for browsing and normal office use.

To the experts in here:
How can it be that the CPU fails so hard at some FFT lengths during the Prime95 benchmark? Is there a way to fix this somehow, or should I just trash this thing?

Thanks in advance!

best regards,
Chris H.
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