verilator_gantt

Verilator_gantt creates a visual representation to help analyze Verilator multithreaded simulation performance, by showing when each macro-task starts and ends, and showing when each thread is busy or idle.

For an overview of use of verilator_gantt, see Code Profiling.

Gantt Chart VCD

Verilated_gantt creates a value change dump (VCD) format dump file which may be viewed in a waveform viewer (e.g. C<GTKWave>):

_images/fig_gantt_min.png

Fig. 2 Example verilator_gantt output, as viewed with GTKWave.

The viewed waveform chart has time on the X-axis, with one unit for each time tick of the system’s high-performance counter.

Gantt Chart VCD Signals

In waveforms there are the following signals. In GTKWave, using a data format of “decimal” will remove the leading zeros and make the traces easier to read.

evals

Increments each time when eval_step was measured to be active. This allow visualization of how much time eval_step was active.

eval_loop

Increments each time when the evaluation loop within eval_step was measured to be active. For best performance there is only a single evaluation loop within each eval_step call, that is the eval_loop waveform looks identical to the evals waveform.

measured_parallelism

The number of mtasks active at this time, for best performance this will match the thread count. In GTKWave, use a data format of “analog step” to view this signal.

predicted_parallelism

The number of mtasks Verilator predicted would be active at this time, for best performance this will match the thread count. In GTKWave, use a data format of “analog step” to view this signal.

cpu#_thread

For the given CPU number, the thread number measured to be executing.

mtask#_cpu

For the given mtask id, the CPU it was measured to execute on.

thread#_mtask

For the given thread number, the mtask id it was executing.

predicted_thread#_mtask

For the given thread number, the mtask id Verilator predicted would be executing.

verilator_gantt Arguments

<filename>

The filename to read data from, defaults to “profile_exec.dat”.

--help

Displays a help summary, the program version, and exits.

--no-vcd

Disables creating a .vcd file.

--vcd <filename>

Sets the output filename for vcd dump. Default is “verilator_gantt.vcd”.