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-   -   CPU Time using time command of unix (http://www.cfd-online.com/Forums/main/5395-cpu-time-using-time-command-unix.html)

Vinay Kumar November 10, 2002 12:56

CPU Time using time command of unix
 
I want to compare the performance of two different programs for matrix inversion. Somebody suggested me that one can do so by comparing CPU time using time command ($time a.out). But it gives three times (real, user, sys) and I don't understand which time is to be compared.

Please help.

Thanks.

Amit

boling November 10, 2002 13:28

Re: CPU Time using time command of unix
 
Most time the following relation is correct. real = user + system I always use user time if I am trying to tune the code, just like your current situation . But for actual purpose , for example , the total runnning time of my RANS3D code, I just use real time.

Wei November 12, 2002 09:42

Re: CPU Time using time command of unix
 
"user" time is the CPU time used to perform any tasks in so-called user space (including all the actual calculation etc). "system" time is the CPU time used to perform any system calls in the kernal space (such as "read" or "write" system call).


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