Hi,

I recently upgraded from nest v2.2.2 to v2.20.1 and experienced a decrease in simulation speed. I tested it using the /brunel_alpha_nest.py/ example script that is available in both versions. For better comparison I set the option /to_file/ in the new version to /False/.

Simulating the network for 10s using v2.2.2 I get: 100 %: network time: 9999.0 ms, realtime factor: 0.0672

Simulation finished. Brunel network simulation (Python) Number of neurons : 12500 Number of synapses: 15637600       Exitatory  : 12512500       Inhibitory : 3125000 Excitatory rate   : 28.84 Hz Inhibitory rate   : 28.78 Hz Building time     : 5.56 s Simulation time   : 149.01 s

Using v2.20.1: 100 %: network time: 9999.0 ms, realtime factor: 0.0601

Simulation finished. Brunel network simulation (Python) Number of neurons : 12500 Number of synapses: 15637600       Exitatory  : 12512500       Inhibitory : 3125000 Excitatory rate   : 28.84 Hz Inhibitory rate   : 28.78 Hz Building time     : 2.39 s Simulation time   : 168.58 s

Adding /'total_num_virtual_procs': 48/and running it for 100s on a 48 core node using v2.2.2 I get: Simulation time   : 98.49 s

Using v2.20.1: Simulation time   : 120.08 s

Both versions are build with OpenMp support and without mpi. Is this expected or do you have any idea where this behavior comes from?

Thank you in advance!

Best, Hartmut