Built-in timers

Basic timers

Basic built-in timers keep track of the time NEST spent for network construction and actual simulation (propagation of the network state). These timers are active in all simulations with NEST, and the measured times can be checked by querying the corresponding kernel attributes. For example:

nest.time_simulate

The following basic time measurements are available:

Name

Explanation

time_construction_create

Cumulative time NEST spent creating neurons and devices

time_construction_connect

Cumulative time NEST spent creating connections

time_simulate

Time NEST spent in the last Simulate()

Note

While preparing the actual simulation after network construction, NEST needs to build the pre-synaptic part of the connection infrastructure, which requires MPI communication (Jordan et al. 2018). This happens only for the first call to Simulate() unless connectivity changed in the meantime, and it may cause significant overhead by adding to time_simulate. Therefore, the cumulative time NEST spent for building the pre-synaptic connection infrastructure is also tracked by a basic timer and available as kernel attribute time_communicate_prepare.

In the context of NEST performance monitoring, other useful kernel attributes are:

Name

Explanation

biological_time

Cumulative simulated time

local_spike_counter

Number of spikes emitted by the neurons represented on this MPI rank during the last Simulate()

Note

nest.ResetKernel() resets all time measurements as well as biological_time and local_spike_counter.

Detailed timers

Detailed built-in timers can be activated (and again deactivated) prior to compilation through the CMake flag -Dwith-detailed-timers=ON. They provide further insights into the time NEST spends in different phases of the simulation cycle, but they can impact the runtime. Therefore, detailed timers are by default inactive.

If detailed timers are active, the following time measurements are available as kernel attributes:

Name

Explanation

Part of

time_gather_target_data

Cumulative time for communicating connection information from postsynaptic to presynaptic side

time_communicate_prepare

time_communicate_target_data

Cumulative time for core MPI communication when gathering target data

time_gather_target_data

time_update

Time for neuron update

time_simulate

time_gather_spike_data

Time for complete spike exchange after update phase

time_simulate

time_collocate_spike_data

Time to collocate MPI send buffer from spike register

time_gather_spike_data

time_communicate_spike_data

Time for communicating spikes between compute nodes

time_gather_spike_data

time_deliver_spike_data

Time to deliver events from the MPI receive buffers to their local synaptic targets (including synaptic update, e.g. STDP synapses) and to the spike ring buffers of the corresponding postsynaptic neurons

time_gather_spike_data