SimScale CAE Forum

Difference between the write options


#1

Hey,
its possibly an easy question, but i cant manage it. My question is about the different write options and the write steps.
I tryed to creat an excel table, to represent the write behavior.
The chosen sim. time is 3 seconds, the simulation needs 2 seconds in real time.
The X represents a write for the post-proseccing.

  1. Are the write steps at the table correct ? I hope its not to confusing :slight_smile:

  2. What is the difference between, measured by the cpu and computing machine ?

  • Clock time : Specifies the write interval via the real time, measured on the computing machine
  • CPU time : Specifies the write interval via the real time, measured by the CPU

is it not the same, can the CPU have a different time as the rest of the system ?

I am very grateful if you answer my questions

Kai


#2

Hey Kai,

Nice to see you back :slight_smile: So regarding the time question (which I will answer first, for the first one I will have a closer look at it later this day) the CPU time is the time the processor(s) spends on the task which does not necessarily mean that it is used each second for instance when writing on the disk or other tasks not related to the CPU. The Clock time is simply the time you know and you live by :smiley: I am sure @Retsam can add some additional thoughts on this as a retired software engineer. :slight_smile:

Cheers,

Jousef


#3

Hi @Kai_himself: I would like to help but it can be possible if I understand your problem. Real time (wall time) / CPU time relation is tied to number of processors used. Efficiency of distributed workload is not linear, it is rather like N^2. :thinking:

So called simulation time’ in seconds, when your write resolution is one second (writing every second), is rather a convention. If you divide simulation time by 10, but keep the same number of steps, you would write with restitution of 0.1 second. Obviously, ‘wall time’ or’clock time’ would remain the same. Also the same amount of CPU would be needed. But then you will think that for 10 seconds simulation you need 100 seconds of CPU time… But here I simply over guess your intentions…

Cheers,

Retsam


#4

thank you both for your answers, now i understand it :).
Greetz
Kai