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argir April 15, 2009 13:27

F3D v9.3
Hi everyone. I am using F3D v.9.3 SMP on Core i7 platform. I am comparing CPU usage on Core 2 Duo and Core 2 Quad. The CPU usage on Core 2 Duo and Core 2 Quad is 100% but on Core i7 CPU usage is 60-70%. Could anyone explain why?

PS. I am also using MP version on two Xeon Quad and it is using 100% of CPUs.

H.C April 15, 2009 14:31

are you running the same input files on all machines? how many cores did you specify in the input files? The core i7 machine might have hyper-thread tech, and if there are 4 cores, the windows will think it has 8 cores. That might be the reason why you only see 60% or 70% on i7 machine.

argir April 15, 2009 15:11

Of course I am using the same prepin file and stl file. I am using “All available processors” so it shows 8 processors in solver. I was thinking that it could be due to RAM but 6Gb is quite enough. Do you mean that Core i7 is only 10-20% faster than Core 2 Quad? But here is another question why the CPU usage is not 100%. I am conceding that Core i7 is not two times faster but F3D is not using 100% of CPU? Is it due to unoptimized architecture? (I read about that (couple mathematical software) in reviews)

H.C April 15, 2009 18:11

As mentioned, becoz of the hyper-thread tech, even though windows reports that there are 8 cores, it only has 4 real cores, and as flow3d is a computationally intensive program, the 4 real cores will be fully occupied during a simulation and the other 4 hyper-thread cores normally don't have much chance to be utilized. That's probably why it cannot reach 100% usage sometimes.

As for how faster the core i7 is compared to core2 quad, I dont many details, and more info on the CPU codes is needed. But for some certain case setup (with the same numerical method and number of cores), it was noticed that core i7 965 can be 2x faster than core2 quad Q9650.

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