I needed to get SMPPSim to run faster. With the default (or near default) settings, I was barely getting 2-2.5 (added up) requests per second from two kannels connected to one SMPPSim.
Setting the following settings increased my throughput to around 30-50 requests per second. YMMV since your hardware and test setup won't be the same as mine. Among other things I'm testing with DLRs in postgresql 8.2 in an Ubuntu gutsy VirtualBox instance. I could probably get better performance out of a gutsy LXC instance but the Gutsy repos aren't around anymore so I can't create a gutsy instance :-). And I'm too lazy to build 8.2 from source :-).
I also changed this setting but mainly to silence kannel whining about TLVs it didn't recognize. It should not affect SMPPSIM performance.
I wanted to speed up receiving DLRs too and the default settings were too slow (certainly the message state check frequency was far too high). These are my DLR related settings now.
This is just to slightly reduce some noise due to messages being kept around in the queue even though they've really been processed completely.
I don't remember the default value for this. I had it at 5 though, probably me not reading the bit that it's in ms :-).