Tools for quantitative systems performance analysis?

I have a model of a simple distributed system as a heterogeneous network of a number of producers and consumers of various classes of workitem, and a number of compute nodes which can process those workitems at various rates. There are arcs connecting the nodes introducing latencies and bandwidth limits.

What I'm looking for is some practical tool I can describe the model to (as a DSL, or with a graphical editor), along with the statistical distribution of workitems for processing, and which can then chomp on my model (analytically or by simulation) and tell me things about the throughput statisti开发者_开发技巧cs (e.g average throughput, how often certain response-time thresholds are exceeded etc). Does such a tool exist ?

Seems what I was looking for falls under the general heading of Discrete Event Systems.

SimPy looks like a nice tool for simulating such things.