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Old 2004-07-10, 14:52   #1
optim's Avatar
Nov 2003
European Union

23×13 Posts
Exclamation why 45% CPU utilisation?

I am running MPrime (the Linux version of Prime95) on a computer with 512MB RAM.

Top (similar to task manager in Windows) reported MPrime used about 45% of the CPU. But no other process was using the CPU, so I thought something went wrong.

Top reported high memory utilisation by MPrime so I understood MPrime was performing P1 calculations which require too much memory.

I found quickly the misconfiguration: Because the computer had 1GB of memory when I installed MPrime on it, I configured it to use a maximum of 888MB RAM. Now with only 512MB RAM, MPrime was eating all available memory and somehow it was not using the full power of the CPU. After I updated the configuration of MPrime to use 384MB RAM maximum, I checked again through top and it reported near 98-99% CPU utilisation. Problem solved.

I posted this in order to let other people know of this behaviour and fix their systems, if they encounter the same problem sometime.

And now the question: Why only 45% CPU utilisation (with no other process eating cpu power)? I know the problem was the memory, but how it is explained technicaly?
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Old 2004-07-10, 16:58   #2
dsouza123's Avatar
Sep 2002

2·331 Posts

MPrime has to wait (idled) while the OS retreives paged out memory.

Your hard disk was getting a workout.
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