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>):
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.