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 utrace 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.

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