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

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.

"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).