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-   -   Effect of added CPU ? (http://www.cfd-online.com/Forums/main/1062-effect-added-cpu.html)

steve podleski July 21, 1999 10:29

Effect of added CPU ?
 
I have a Polywell PC workstation with a dual CPU motherboard which has only one CPU installed. I do grid generation or run a CFD code on that machine which has 512Mb of RAM.

Running 3D CFD code (NPARC3D) with a grid of approx. 1.2M grid points slows the machine down considerably in that running a mesh gen code, such as ICEM-CFD, simultaneously is very slow. We are thinking of adding the second CPU. BTW, about 300Mb of RAM is available when the CFD code is running which is more than enough for the mesh gen.

I know that this is a CFD forum but the influence of computer hardware on CFD is considerable and many CFDers are very knowledgeable about computer hardware.

My question is: will the addition of this second CPU double or almost double the speed of interaction with the mesh generator as the CFD code is running? The CFD code is not a code that can choose a specific CPU and I suspect that the mesh gen ICEMCFD does not either.

John C. Chien July 21, 1999 12:20

Re: Effect of added CPU ?
 
(1). TWO CPU IS JUST LIKE TWO MACHINES. (2). YOU CAN PUT ONE JOB ON ONE MACHINE (FIRST CPU), AND THE SECOND JOB ON THE OTHER MACHINE (SECOND CPU). (3). YOU MUST HAVE AT LEAST ENOUGH RAM TO COVER EACH JOB. (4). RUNNING TWO JOBS OR MORE ON ONE MACHINE (ONE CPU) IS MULTITASKING. EACH JOB SHARES THE CPU TIME WITH THE OTHER JOB. (5). THE FIRST REQUIREMENT TO SPEEDUP A JOB IS TO HAVE ENOUGH RAM. (6). PC IS RELATIVELY CHEAP NOW, GET ANOTHER MACHINE TO RUN ANOTHER APPLICATION. IT IS FASTER THIS WAY. (SORRY TO ANSWER THE QUESTION IN THIS FONT.) (7). MOST COMMERCIAL CODES WERE NOT WRITTEN SPECIFICALLY FOR PC OR EFFICIENTLY TO SAVE RAM.

steve podleski July 21, 1999 15:48

Re: Effect of added CPU ?
 
John:thanks for the response. I just priced a second PIII 550Mhz cpu at about $500 which is much cheaper than another PC since the CFD code only uses half of the available RAM.

With Windows NT, how can I put the CFD job on one cpu and the mesh gen interactive job on the other cpu? From what some other people tell me, it seems that Windows NT will do distribute the jobs itself and balance the load between the two cpus.

John C. Chien July 21, 1999 16:22

Re: Effect of added CPU ?
 
(1). Well, it is cheaper to just buy a second CPU. (2). Then you don't know whether it will work by itself. I had used a HP workstation with two CPU, and I didn't have to worry about the detail processes involved. (3). Talk to the computer manufacture ( or the mother board manufacture) directly, to see how to get it working.

Nuray Kayakol July 22, 1999 02:58

Re: Effect of added CPU ?
 
I am Windows NT user. I have IBM PC with a dual CPU motherboard which has two CPU installed. I can run two different program at the same time. Each CPU process each job. When you run one program,only one CPU will process the code. The other will be idle. As John said you can use both of the CPU for one job by using multithreading which requires code modification.

The statement "Windows NT will do distribute the jobs itself and balance the load between the two cpus" is true if the programs are independent from each other. NT just distribute the two CPUs to two different job. The meaning of load balance for NT is the use of Set priority option (Real time, high, normal low) in order to one CPU sharing between different jobs(running a program, using a word editor, etc.).


steve podleski July 27, 1999 09:21

Re: Effect of added CPU ?
 
Nuray: Thank you very much for offering your experience with Windows NT and a 2cpu machine. You mention the 'Set priority option'; how does one access and use this option?

Nuray Kayakol July 27, 1999 09:45

Re: Effect of added CPU ?
 
here is the steps (1) open the task manager (2)select the process tab (3)select the image name which belongs to your *.exe file (4)click right hand side button of mouse then select "set priority" icon. (5)you may then select one or two CPU for your process.

I think this may help to you. If not, please do not hesitate to ask more question.

Best Regards

Nuray

steve podleski July 27, 1999 10:24

Re: Effect of added CPU ?
 
Nuray: Thank you very much for offering your experience with Windows NT and a 2cpu machine. You mention the 'Set priority option'; how does one access and use this option?

clifford bradford August 10, 1999 20:26

Re: Effect of added CPU ?
 
steve, i read your message both here and on a newsgroup. i responded on the newsgroup but i don't know if you read it. before you try to run windows software on a shared memory 2 cpu computer you must ensure that the processes will be run exclusively on a given processor. windows nt will not do this. for the code to work in this manner the source code must be modified. in any case the performance will still be compromised since the 2 cpus will be sharing the same memory (RAM). a second computer may not be as expensive as you think. since you'll be using the computer exclusively for this role you can have a computer custom built for you, all it should need is a motherboard, ram, hard drive and an ethernet card (i assume that's what you use) you don't even need a keyboard, screen or mouse for it as you'll strictly be doing batch jobs. if the suppliers of code can guarantee that the code (or a customised version of it) will run as you want then go ahead. but i doubt that this will be the case. as far as i know windows nt balances loads by using the cpus opportunistically and not exclusively.


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