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 ?
Moderators: Global Moderator, Moderator
-
VASP001
- Jr. Member
- Posts: 72
- Joined: Tue Oct 27, 2009 2:56 pm
- License Nr.: 176, upgraded to paw
- Location: Hefei National Laboratory for Physical Sciences at the Microscale
What do this time mean ?
Last edited by VASP001 on Sun Dec 27, 2009 1:28 am, edited 1 time in total.
-
pkroll
- Newbie
- Posts: 28
- Joined: Tue Jun 14, 2005 2:48 pm
What do this time mean ?
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.
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.
Last edited by pkroll on Sun Dec 27, 2009 4:28 am, edited 1 time in total.