question about the correlation between timestep and computational efficiency

Hi, everyone, I have a question about the correlation between timestep and computational efficiency. I just run two simulations. The timestep used in the 1st simulation is 1fs, and the 2nd is 2 fs. All the other parameters are same for both simulations. The 1st simulation need 33 hours to run 1000,000 steps. But the 2nd simulation just need 17 hours to run 1000,000 steps.
I don’t know why the computational efficiency enlarge? Can you answer my question, thanks very much!

Hi, everyone, I have a question about the correlation between timestep and computational efficiency. I just run two simulations. The timestep used in the 1st simulation is 1fs, and the 2nd is 2 fs. All the other parameters are same for both simulations. The 1st simulation need 33 hours to run 1000,000 steps. But the 2nd simulation just need 17 hours to run 1000,000 steps.
I don’t know why the computational efficiency enlarge? Can you answer my question, thanks very much!

Were both calculations run under the exact same conditions?
Same hardware, same executable, same OS, no other users and calculations?

Sharing a machine with some “parasite” job is the most likely explanation for the slowdown of the first job.

Axel

Hi, Axel, Thanks very much for your help. Both my calculations run under the same conditions. Yesteday I run another simulation. It might need 33 hours for 1000,000 steps again. It is very strange. I will try more simulations to find the reason.
Best wishes

Hi, Axel, Thanks very much for your help. Both my calculations run under the
same conditions.

how do you check it? how can you prove that there isn't something else
going on on the machine(s) that you are running on that you don't
control?

Yesteday I run another simulation. It might need 33 hours
for 1000,000 steps again. It is very strange. I will try more simulations to
find the reason.

i would be *extremely* surprised that it is due to the simulation and
particularly the choice of time step. if anything a larger timestep
will require more time for the same number of steps, because it would
require more frequent neighbor list updates.

the only way how i can imagine to have that big differences in run
times for otherwise identical inputs would be when your system has a
severe load imbalance. but that rarely results in a doubling of the
walltime. using a node that has a rogue runaway job or something
equivalent on it, is a much more likely explanation.

axel.