verilator_gantt

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

For an overview of the 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>):

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, use “decimal” data format to 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; the default is “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; the default is “verilator_gantt.vcd”.