Page 1 of 1
What do this time mean ?
Posted: Sun Dec 27, 2009 1:28 am
by VASP001
Total CPU time used User time System time Elapsed time
And which factors determine those time ?For example ,the communication between the nodes ,and the nodes used in the computation .
What do this time mean ?
Posted: Sun Dec 27, 2009 4:28 am
by pkroll
Grossly speaking: User + System == CPU (approx., and most often).
Elapsed == Wall clock time since the program started.
System = usually small – it's what the system does with your job besides executing commands [swapping, paging (?!)]
User = that's what counts. Herein is everything of your job included. That means, all executions, all communications, all waits for synchronization of procs in multi-CPU jobs, etc.
You will need to check timing.c in vasp.4.lib or vasp.5.lib. It calls two system routines: getrusage [see <sys/resource.h>] and gettimeofday [see <sys/time.h>].
If you study the structures of these functions – and consider their implementation in your system [OS, MPI] – it will give you some detailed insight.
If you want more detailed information about your job (e.g., timing how much is spend for communication), you need to attach/use some performance analyzer.