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The --prof-threads option has been split into two independent options:
1. --prof-exec, for collecting verilator_gantt and other execution
related profiling data, and
2. --prof-pgo, for collecting data needed for PGO
The implementation of execution profiling is extricated from
VlThreadPool and is now a separate class VlExecutionProfiler. This means
--prof-exec can now be used for single-threaded models (though it does
not measure a lot of things just yet). For consistency VerilatedProfiler
is renamed VlPgoProfiler. Both VlExecutionProfiler and VlPgoProfiler are
in verilated_profiler.{h/cpp}, but can be used completely independently.
Also re-worked the execution profile format so it now only emits events
without holding onto any temporaries. This is in preparation for some
future optimizations that would be hindered by the introduction of function
locals via AstText.
Also removed the Barrier event. Clearing the profile buffers is not
notably more expensive as the profiling records are trivially
destructible.
88 lines
2.5 KiB
ReStructuredText
88 lines
2.5 KiB
ReStructuredText
.. Copyright 2003-2022 by Wilson Snyder.
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.. SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
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verilator_gantt
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===============
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Verilator_gantt creates a visual representation to help analyze Verilator
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multithreaded simulation performance, by showing when each macro-task
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starts and ends, and showing when each thread is busy or idle.
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For an overview of use of verilator_gantt, see :ref:`Profiling`.
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Gantt Chart VCD
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---------------
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Verilated_gantt creates a value change dump (VCD) format dump file which
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may be viewed in a waveform viewer (e.g. C<GTKWave>):
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.. figure:: figures/fig_gantt_min.png
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Example verilator_gantt output, as viewed with GTKWave.
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The viewed waveform chart has time on the X-axis, with one unit for each
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time tick of the system's high-performance counter.
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Gantt Chart VCD Signals
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-----------------------
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In waveforms there are the following signals. In GTKWave, using a data
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format of "decimal" will remove the leading zeros and make the traces
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easier to read.
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evals
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Increments each time when eval_step was measured to be active. This
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allow visualization of how much time eval_step was active.
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eval_loop
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Increments each time when the evaluation loop within eval_step was
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measured to be active. For best performance there is only a single
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evaluation loop within each eval_step call, that is the eval_loop
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waveform looks identical to the evals waveform.
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measured_parallelism
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The number of mtasks active at this time, for best performance this will
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match the thread count. In GTKWave, use a data format of "analog step" to
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view this signal.
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predicted_parallelism
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The number of mtasks Verilator predicted would be active at this time,
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for best performance this will match the thread count. In GTKWave, use a
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data format of "analog step" to view this signal.
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cpu#_thread
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For the given CPU number, the thread number measured to be executing.
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mtask#_cpu
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For the given mtask id, the CPU it was measured to execute on.
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thread#_mtask
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For the given thread number, the mtask id it was executing.
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predicted_thread#_mtask
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For the given thread number, the mtask id Verilator predicted would be
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executing.
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verilator_gantt Arguments
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-------------------------
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.. program:: verilator_gantt
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.. option:: <filename>
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The filename to read data from, defaults to "profile_exec.dat".
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.. option:: --help
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Displays a help summary, the program version, and exits.
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.. option:: --no-vcd
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Disables creating a .vcd file.
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.. option:: --vcd <filename>
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Sets the output filename for vcd dump. Default is "verilator_gantt.vcd".
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