[gmx-users] what is meaning of vol 0.95 imb F 1%?

Berk Hess gmx3 at hotmail.com
Thu Apr 30 12:49:08 CEST 2009

> Date: Thu, 30 Apr 2009 11:33:24 +1000
> From: Mark.Abraham at anu.edu.au
> To: gmx-users at gromacs.org
> Subject: Re: [gmx-users] what is meaning of vol 0.95 imb F 1%?
> wuxiao wrote:
> > Dear gmx users,
> >   If -v was passed on to mdrun, such rows  one by one would be printed 
> > continuously as follows:
> > vol 0.95 imb F 1% step 1000, will finish Thu Apr 30 15:39:33
> >   Obviously, the words "step 1000, will finish Thu Apr 30 15:39:33" mean 
> > that the current running step is 1000, the whole run will finish at 
> > 15:39:33, on Thuseday, April 30th. But what it is meant by "vol 0.95 imb 
> > F 1%"? Thank you very much for any reply.
> This is the verbose output produced under dynamic load balancing and
> domain decomposition. A quick look at the code didn't make it clear what
> "vol" means (it's some kind of DD workload measure, though), and "imb F"
> is the load imbalance between different processors in calculating the
> forces. I guess that if the two values are reasonably close to 1 and 0%
> respectively, then things are fine.
> Mark

I just realized I never documented this output.
vol gives the smallest volume of a DD cell relative to the average volume.
This is a measure of the load density differences in your system.
It does not have to close to 1. If it is very small, it just means that
your system would be very load imbalanced when you would run it without
load balancing.
The can also be an exclamation mark after the volume. This means that
the load balancing was limited by the minimum cell size in one or more dimensions
and some cells can not be made smaller, in the log file you can then find more details.


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