# u_trace GPU Performance Tracing

Mesa has its own GPU performance tracing framework which drivers may choose to implement. `gpu.renderstages.*` producer for Perfetto Tracing is based on u_trace.

It doesn’t require external dependencies and much simpler to use. Though it provides information only about GPU timings and is harder to analyze for complex rendering.

u_trace is useful when one needs to quickly identify performance bottleneck, or to build a tool to analyze the raw performance data.

Drivers which support u_trace:

  - Intel drivers: ANV, Iris

  - Adreno drivers: Freedreno, Turnip

## Usage

u_trace is controlled by environment variables:

MESA_GPU_TRACES

  controls whether u_trace is enabled and trace output

  `print`

    prints in a human readable text format. It should be noted that this is mutually exclusive with `print_json` and both cannot be enabled at the same time.

  `print_json`

    prints in JSON format, suitable for parsing. Application should appropriately finish its rendering in order for trace’s json to be valid. For the Vulkan API, it is expected to destroy the device, for GL it’s expected to destroy the context.

  `perfetto`

    enables Perfetto instrumentation prior to connecting, Perfetto traces can be collected without setting this but it may miss some events prior to the tracing session being started.

  `markers`

    enables marker instrumentation, will print trace markers into the CS which can then be viewed by dumping the CS from the driver.

    > - For Turnip, `cffdump` can be used to view the markers in the trace.

  `indirects`

    enables indirect data capture for some of the tracepoints (like indirect draw count or indirect dispatch size)

MESA_GPU_TRACEFILE

  specifies a file where to write the output instead of `stdout`

*_GPU_TRACEPOINT

  tracepoints can be enabled or disabled using driver specific environment variable. Most tracepoints are enabled by default. For instance `TU_GPU_TRACEPOINT=-blit,+render_pass` will disable the `blit` tracepoints and enable the `render_pass` tracepoints.

  Driver | Environment Variable | Tracepoint Definitions
  --- | --- | ---
  Freedreno | FD_GPU_TRACEPOINT | `src/gallium/drivers/freedreno/freedreno_tracepoints.py`
  Turnip | TU_GPU_TRACEPOINT | `src/freedreno/vulkan/tu_tracepoints.py`
  ANV | INTEL_GPU_TRACEPOINT | `src/intel/vulkan/intel_tracepoints.py`