Flow Monitor taking too long

[Soulimane Mammar]

Hi,

I'm trying to collect some stat data using Flow Monitor. The problem is that even with a very simple topology (2 nodes) and a simulation time of 15 sec the process is taking too much time (till now the simulation is running for several hours and no results back yet)

Is this normal ?

Regards

[Gabriel]

Not normal. Did you set Simulator::Stop(Seconds(15.0))?
Or maybe you did one infinite loop? If it is just a for, easy to find with a debugger.

Otherwise, use a profiler to find out where the program is spending its time. If you're on linux, try sysprof: https://wiki.gnome.org/Apps/Sysprof 

[Soulimane Mammar]

No, in my script all the applications stop sending their traffic within 15 sec (so in theory after 15s there will be no events ).

After several hours the simulation crashed with  the message error 

assert failed. cond="next.key.m_ts >= m_currentTs", -0.709551616s -1 file=../src/core/model/default-simulator-impl.cc, line=143
terminate called without an active exception

Syprof shows that the Flow Monitor is consuming almost all cpu cycles (see attached screenshot)

[Soulimane Mammar]

After all, I had to explicitly add Simulator::Stop() to my simulation script and not counting on the fact that after the applications stop the event list will be empty

[Gabriel]

Based on the assert, you just had an overflow (negative timestamps).
Based on sysprof, you would never run out of events since Flow Monitor is creating more to check the network periodically.

[Soulimane Mammar]

Flow Monitor is an outside observer and in theory it should not place events. In practice, I guess this is not possible unless implementing a meta simulator that runs the simulator itself and any other observer entity

[Gabriel Ferreira]

I do agree. Maybe we could count non-observing events in the event queue and interrupt the simulation if it ever reached 0, assuming observing events can't schedule a non-observing event.
Doesn't sound that bad in terms of performance and should work fine in most cases. 

[Soulimane Mammar]

Sounds Great. As soon as I'll finish my actual work, perhaps I'll dedicate some time to contribute to ns3 code ;-)