Span tracing

[adam-singer]

Description

Adding feature to enable/disable builds of nativelink to include trace spans.

Trace spans can be use for instrumenting historical call paths of the tokio workers. Implementation provided shunts enabling/disabling at the cfg/features flags level. Enabling this feature would have performance runtime impact and should be used in debugging/introspection scenarios. Applying the instrumentation updates the source tree and not expected to be checked in (atm). The span format uses chrome tracing json and can be viewed in chrome://tracing (or https://ui.perfetto.dev/). Trace snapshots are collected upon sever exit.

Output traces upon server exit are dumped in the cwd of the nativelink bin in the format trace-*.json

Example

# Apply instrumentation
./tools/patch_tracing.sh fix
# Build/Run
RUST_LOG=INFO cargo --config 'build.rustflags=["--cfg", "tokio_unstable", "--cfg", "enable_tracing"]' run --features enable_tokio_console,enable_tracing -- nativelink-config/examples/basic_cas.json
# Unapply instrumentation
./tools/patch_tracing.sh strip

Open Questions

Should trace snapshots be collected upon server exit, client requests or external signal to admin ports?

Should clippy-tracing be a preinstalled expectation or configured/added in nix?

Should we checkin the tracing macro and create linting that auto lints (fix) the source tree when instrumentation is missing?

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Please also list any relevant details for your test configuration

Checklist

• [ ] Updated documentation if needed
• [ ] Tests added/amended
• [ ] bazel test //... passes locally
• [ ] PR is contained in a single commit, using git amend see some docs

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Name	Status	Preview	Comments	Updated (UTC)
nativelink-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 10, 2024 9:14pm

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