running Fortran code on Linux

[phil]

On May 10, 2005, at 1:12 PM, Michael Yang wrote:

>  I have a CFD Fortran code running on both Windows and Linux 
> platforms. It surprised me that on windows system the code can use up 
> to 50% cpu, while it can use only about 10% cpu in the linux system 
> even there is no other program running. More than 80% of cpu is idle. 
> BTW, both computers have intel 3GHz cpu. I am wondering if anyone has 
> experience in programming under Linux enviroment. How can I make most 
> use of the system resources, i.e., cpu, memory etc. Does my problem 
> come from the code itself or from other things like the compiler etc.

Since I don't know what your program is actually doing, I can only 
answer in generalities...so here they are.  :-)

A running program is either computing or waiting for something.  The 
standard approach to problems like yours is to profile, trace, or 
otherwise determine what it's waiting on when it's not using the CPU.  
Sometimes waiting is a really good thing...for example, if an HTTP 
server spends a lot of time waiting for requests, it's doing its job 
well.  However, if it's waiting for disk reads/writes or other 
peripheral access, that points a way to speeding things up.  (I'm 
assuming these are not multi-processor systems; that would change some 
things.)

You don't say whether there's a difference between the systems in the 
actual amount of work completed within a constant amount of time.  (?)

........................
Phillip Mills
Multi-platform software development
(416) 224-0714

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