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CPU time Vs Wall clock time

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Old   February 26, 2012, 01:06
Unhappy CPU time Vs Wall clock time
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Dear CFX users ,

In my one desktop(windows7), processor 1.86Ghz, RAM 4 GB, 64bit OS, I am trying to do a simulation with 1.6 million mesh. I have found that last 2days ago I start a transient simulation at night around 7 o clock and when I came back nextday at my workplace 9o clock morning and found that it is completed only 17 time steps in last 14 hrs . Moreover I have checked that the total cpu time and total wall clock time is not same in CFX solver manager.

Same simulation I started yesterday at day time watch what happened and saw that full simulation take 8 hrs to finish 400 time step but every hour I have checked whether simulation is working or not.

Today still same problem occured after certain time period I think simulation stopped and whenever I check simulation , move cursor then it starts calculation. Additionally I have checked that during simulation run time CPU usages showing 50% and physical memory is showing 35% in this dual core machine.

I am confused why this is happening because in my another desktop with windows XP, 3.25Gb RAM, if I start any simulation(400,000 mesh) and checked that it is finished all time step without any problem, I mean it is not idle.

Is this problem arises from my this system or anything need to change in windows 7.

If anybody help me to find out the problem then it would be good for me.


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Old   February 26, 2012, 05:06
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Glenn Horrocks
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Most probably you have filled the physical RAM and it is using the page file (hard drive). This is far slower than physical RAM so the simulation will proceed very slowly. When you start a new run you should look at the task manager (or top for the linux types) to check the run starts OK and grabs a full CPU worth of power. If the CPU load is struggling then you probably have run out of RAM.
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Old   February 28, 2012, 20:06
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Thanks Glenn for your quick advice. Sounds like I need to change my system configuration mainly RAM.


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