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