Performance of NS

[Wei Tsang Ooi <weitsang@cs.cornell.edu>]

Hi,

Is anyone working on improving the performance of ns ?

IMHO, a lot of design decisions in ns are made to allow
rapid-prototyping but not high performance.  As a result,
ns crawls when the simulated network is large.

Below are some ideas I am exploring, but I am not familiar
with ns enough to make any changes and still be sure that
no others will be affected.

- profiles the otcl code in ns, and identify bottlenecks.
  it should not be too difficult to insert code into otcl
  to see how many times each Otcl instproc is called, and
  how long each call takes.  

- optimizes the bottleneck somehow.  For example, I believe
  "set" and "instvar" are the most common calls.  Is there a
  way to speed these up (like by-passing the lookup) ?

- can some of the otcl code be moved into C++  space ?
  For example, Node::add-route is called O(n^2) time
  in Simulator::compute-flat-route, and is a major bottleneck
  in start-up time.

- plain and simple code optimization.  For example, the current
  Timer class (tcl/mcast/timer.tcl) makes many redundant calls
  to "$ns cancel $id".  Also, we should be able to make 
  RouteLogic::compute_routes() run faster.

Any comments ?
-- 
______________________________________________________________
weitsang@cs.cornell.edu  System Lab, Upson Hall (607) 255-0102