i7's over estimating claimed credit

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skildude
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Joined: 18 Jul 08
Posts: 57
ID: 25792
Credit: 522,106,329
RAC: 387,115

I've been following my own progress on the 321 llr challenge and noticed that the i7 computers are all claiming about 2X what every other intel and AMD chip is claiming. I'm beginning to wonder if their is something wrong with the chips. My computer and others routinely claims 230-280 credit. the i7's typically claim 400+ and one actually claimed 800+. I'm not one to toss away free extra credit but it seems something is seriously wrong with those processors

ID: 22783 |

Michael Goetz

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Joined: 21 Jan 10
Posts: 13787
ID: 53948
Credit: 345,142,938
RAC: 12,033

I've been following my own progress on the 321 llr challenge and noticed that the i7 computers are all claiming about 2X what every other intel and AMD chip is claiming. I'm beginning to wonder if their is something wrong with the chips. My computer and others routinely claims 230-280 credit. the i7's typically claim 400+ and one actually claimed 800+. I'm not one to toss away free extra credit but it seems something is seriously wrong with those processors

I'm guessing you have hyperthreading enabled?

This is all pure speculation, but I'm guessing I know what's happening. The only thing that doesn't make any sense is that the older Pentium CPUs should also have this problem if they have HT.

When the BOINC benchmarks run, it runs the floating point benchmark on all the cores, and the integer benchmark on one core. No clue why it does that.

I'm guessing that all the work done at Primegrid uses integer math, rather than floating point. Assuming that's true, the only benchmark of interest is the integer benchmark, which is run on only one thread -- so there's no competing thread (running as a hyperthread on the same core) slowing it down.

When the work units are running, however, all the threads are in use, so they run somewhat slower (about 1/3 slower) due to the effects of hyperthreading. That makes the WU consume more CPU time, as if more work was being done. That, combined with the higher integer benchmark score that was not affected by HT, combines to cause a higher reported claimed credit

It's just a guess, and there's more than one assumption that may be incorrect in this theory.

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ID: 22785 |