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how to make Fluent fully utilize CPU power

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Old   March 11, 2007, 22:11
Default how to make Fluent fully utilize CPU power
  #1
aPpA
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I have installed Fluent 6.3 on a dual Xeon 64 bit processor system running Fedora core 6. However when i run fluent it is only using about 50% of the CPU power. Why is'nt fluent using 100% CPU. thanks.
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Old   March 12, 2007, 12:31
Default Re: how to make Fluent fully utilize CPU power
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Seeker Phil
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This is most probably because 'top' or other Process use commands display complete processor information and not for each thread. In effect you are using only one thread when you run fluent. You might have to use Fluent in parallel to make full use of both threads. You will need to define your computer as a single processor/ 2 process system -Phil

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Old   March 12, 2007, 13:22
Default Re: how to make Fluent fully utilize CPU power
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aPpA
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Thanks for the reply Seeker, By 'thread' if you mean CPU, I am only running serial fluent. when i use the command 'top' it shows both the CPU's usage, with the first CPU at about 40% and the other being idle. Anyways..if i run parallel fluent it still is using only 30% from each CPU. ........Anymore suggestions please??
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Old   March 12, 2007, 17:05
Default Re: how to make Fluent fully utilize CPU power
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Seeker Phil
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Yeah, I meant each CPU or 'core' or however you wish to call it. Another thing you could do is to minimze your disk access since this reduces efficient use of your processor time with IO operations. If your grid size is fairly small, it might make more sense to run it serial on one processor rather than parallel. - Phil
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Old   March 12, 2007, 21:48
Default Re: how to make Fluent fully utilize CPU power
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mike moran
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i was about to post a similar question, but thought i would just piggy back this thread.

i am running a single core (with hyperthreading) windows system, and running 6.2.16. as i am iterating, i can see that fluent is using between 46 and 50% of my processor. within the task manager, i have set the task priority to 'High'.

is there anything i can do to make fluent use the remaining 50-ish percent of my processor?

thanks a lot
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Old   March 13, 2007, 00:28
Default Re: how to make Fluent fully utilize CPU power
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Bob
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Hello Mike, I had the same problem in the past. The reason is, that fluent see the hyper threating processor as two processors. You have to disable the hyper threating. I don't now exacatly how it works in different systems. Sometimes there is a software access or you have to do it through the bios of your computer. But be carefully. I suppose to make a backup/image first of your system.
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Old   March 13, 2007, 01:43
Default Re: how to make Fluent fully utilize CPU power
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mike moran
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Thanks for the reply Bob. Disabling hyper-threading isn't a big deal, I can do that in my BIOS quite easily. Seems counter intuitive though, to disable hyperthreading to gain performance?

I guess what I am asking is, by disabling hyper-threading, will I see an increase in performance, or will i just see that 50% move closer to 100%? (CPU usage)
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Old   March 13, 2007, 02:48
Default Re: how to make Fluent fully utilize CPU power
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Charles
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Chances are that you will just see the usage go up to near 100%, but there is unlikely to be a significant change in speed. Some people in the IT industry referred to hyperthreading as hypethreading, with fairly good reason. There are some specially coded apps that benefit from it, but Fluent isn't one of them. I have been told that it is better to leave it off, to avoid any cache contention. Be advised though that parallel Fluent and hyperthreading behave quite differently on Windows and Linux. When I tested it on Windows, running parallel Fluent with hyperthreading (i.e. trying to run 3 or 4 parallel processes on a hyperthreaded dual-processor Xeon) was no quicker than just 2 processes, but at least not much slower either. Under Linux it slowed right down, compared to the 2 process case. So just turn the hypethreading off, it was a blind alley that has now been superceded by multi-core.

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Old   March 19, 2007, 16:34
Default Re: how to make Fluent fully utilize CPU power
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Ahmed
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Fluent License is tied to the number of processors you have, if you have bought a license for one processor, then it will only use one processor even if you have two mounted on the mother board
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