# Perfetto Tracing

Mesa has experimental support for Perfetto for GPU performance monitoring. Perfetto supports multiple producers each with one or more data-sources. Perfetto already provides various producers and data-sources for things like:

- CPU scheduling events (`linux.ftrace`)

- CPU frequency scaling (`linux.ftrace`)

- System calls (`linux.ftrace`)

- Process memory utilization (`linux.process_stats`)

As well as various domain specific producers.

The mesa Perfetto support adds additional producers, to allow for visualizing GPU performance (frequency, utilization, performance counters, etc) on the same timeline, to better understand and tune/debug system level performance:

- pps-producer: A systemwide daemon that can collect global performance counters.

- mesa: Per-process producer within mesa to capture render-stage traces on the GPU timeline, track events on the CPU timeline, etc.

The exact supported features vary per driver:

Supported data-sources
Driver | PPS Counters | Render Stages
--- | --- | ---
Freedreno | `gpu.counters.msm` | `gpu.renderstages.msm`
Turnip | `gpu.counters.msm` | `gpu.renderstages.msm`
Intel | `gpu.counters.i915` | `gpu.renderstages.intel`
Panfrost | `gpu.counters.panfrost` |
V3D | `gpu.counters.v3d` |
V3DV | `gpu.counters.v3d` |

## Run

To capture a trace with Perfetto you need to take the following steps:

1. Build Perfetto from sources available at `subprojects/perfetto` following this guide.

2. Create a trace config, which is a json formatted text file with extension `.cfg`, or use one of the config files under the `src/tool/pps/cfg` directory. More examples of config files can be found in `subprojects/perfetto/test/configs`.

3. Change directory to `subprojects/perfetto` and run a convenience script to start the tracing service:

       cd subprojects/perfetto
       CONFIG=<path/to/gpu.cfg> OUT=out/linux_clang_release ./tools/tmux -n

4. Start other producers you may need, e.g. `pps-producer`.

5. Start `perfetto` under the tmux session initiated in step 3.

6. Once tracing has finished, you can detach from tmux with `Ctrl`+`b`, `d`, and the convenience script should automatically copy the trace files into `$HOME/Downloads`.

7. Go to ui.perfetto.dev and upload `$HOME/Downloads/trace.protobuf` by clicking on Open trace file.

8. Alternatively you can open the trace in AGI (which despite the name can be used to view non-android traces).

To be a bit more explicit, here is a listing of commands reproducing the steps above :

    # Configure Mesa with perfetto
    mesa $ meson . build -Dperfetto=true -Dvulkan-drivers=intel,broadcom -Dgallium-drivers=
    # Build mesa
    mesa $ meson compile -C build

    # Within the Mesa repo, build perfetto
    mesa $ cd subprojects/perfetto
    perfetto $ ./tools/install-build-deps
    perfetto $ ./tools/gn gen --args='is_debug=false' out/linux
    perfetto $ ./tools/ninja -C out/linux

    # Start perfetto
    perfetto $ CONFIG=../../src/tool/pps/cfg/gpu.cfg OUT=out/linux/ ./tools/tmux -n

    # In parallel from the Mesa repo, start the PPS producer
    mesa $ ./build/src/tool/pps/pps-producer

    # Back in the perfetto tmux, press enter to start the capture

### CPU Tracing

Mesa’s CPU tracepoints (`MESA_TRACE_*`) use Perfetto track events when Perfetto is enabled. They use `mesa.default` and `mesa.slow` categories.

Currently, only EGL and the following drivers have CPU tracepoints.

- Freedreno

- Panfrost

- Turnip

- V3D

- VC4

- V3DV

### Vulkan data sources

The Vulkan API gives the application control over recording of command buffers as well as when they are submitted to the hardware. As a consequence, we need to ensure command buffers are properly instrumented for the Perfetto driver data sources prior to Perfetto actually collecting traces.

This can be achieved by setting the `MESA_GPU_TRACES` environment variable before starting a Vulkan application :

    MESA_GPU_TRACES=perfetto ./build/my_vulkan_app

### Driver Specifics

Below is driver specific information/instructions for the PPS producer.

#### Freedreno / Turnip

The Freedreno PPS driver needs root access to read system-wide performance counters, so you can simply run it with sudo:

    sudo ./build/src/tool/pps/pps-producer

#### Intel

The Intel PPS driver needs root access to read system-wide RenderBasic performance counters, so you can simply run it with sudo:

    sudo ./build/src/tool/pps/pps-producer

Another option to enable access wide data without root permissions would be running the following:

    sudo sysctl dev.i915.perf_stream_paranoid=0

Alternatively using the `CAP_PERFMON` permission on the binary should work too.

A particular metric set can also be selected to capture a different set of HW counters :

    INTEL_PERFETTO_METRIC_SET=RasterizerAndPixelBackend ./build/src/tool/pps/pps-producer

Vulkan applications can also be instrumented to be Perfetto producers. To enable this for given application, set the environment variable as follow :

    PERFETTO_TRACE=1 my_vulkan_app

#### Panfrost

The Panfrost PPS driver uses unstable ioctls that behave correctly on kernel version 5.4.23+ and 5.5.7+.

To run the producer, follow these two simple steps:

1. Enable Panfrost unstable ioctls via kernel parameter:

       modprobe panfrost unstable_ioctls=1

   Alternatively you could add `panfrost.unstable_ioctls=1` to your kernel command line, or `echo 1 > /sys/module/panfrost/parameters/unstable_ioctls`.

2. Run the producer:

       ./build/pps-producer

## V3D / V3DV

As we can only have one performance monitor active at a given time, we can only monitor 32 performance counters. There is a need to define the performance counters of interest for pps_producer using the environment variable `V3D_DS_COUNTER`.

    V3D_DS_COUNTER=cycle-count,CLE-bin-thread-active-cycles,CLE-render-thread-active-cycles,QPU-total-uniform-cache-hit ./src/tool/pps/pps-producer

## Troubleshooting

### Tmux

If the convenience script `tools/tmux` keeps copying artifacts to your `SSH_TARGET` without starting the tmux session, make sure you have `tmux` installed in your system.

    apt install tmux

### Missing counter names

If the trace viewer shows a list of counters with a description like `gpu_counter(#)` instead of their proper names, maybe you had a data loss due to the trace buffer being full and wrapped.

In order to prevent this loss of data you can tweak the trace config file in two different ways:

- Increase the size of the buffer in use:

      buffers {
          size_kb: 2048,
          fill_policy: RING_BUFFER,
      }

- Periodically flush the trace buffer into the output file:

      write_into_file: true
      file_write_period_ms: 250

- Discard new traces when the buffer fills:

      buffers {
          size_kb: 2048,
          fill_policy: DISCARD,
      }