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Dead Things - 4x Xeon E7 8860 @ 2267MHz - 5131.5 MPT-score UCBench 2011

Raul SDT

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Good question. Long answer. Apologies in advance.


Windows uses something called "processor groups" to accommodate systems with more than 64 logical processors. With 80 logical processors, the system would be divided into two processor groups comprised of 40 logical processors each. You can manually edit the BCD to change the processor group membership characteristics, but one thing that cannot be changed is the 64-processor ceiling per group.


While this processors group implementation works for parallelized tasks, it does not work for symmetric tasks meaning that you're essentially limited to 64 cores in Windows for any one particular process.


Because UCBench is actually really well-coded, each thread does not leave much processing headroom for hyperthreading, so it benefits way less from HT than, say, wPrime. As such, my score with 32 cores enabled and HT on was way lower than my score with all 40 enabled and HT off.


I had some hope that Server 8 would do away with the clumsy processor group implementation, but that was not the case last time I checked. By comparison, Ubuntu has supported >64 threads per symmetric task since 10.04.

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