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UsingProfiler.md

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id profiler
title Profiler
sidebar_position 20

Profiler

UntoldEngine profiling has two layers that are meant to be used together:

  1. Structured metrics (stable numbers for trends and regressions)
  2. Category logs (on-demand narrative traces for deep debugging)

Use structured metrics as the source of truth, then enable category logs only when you need extra context.

Quick Start

Enable the profiler at runtime:

enableEngineMetrics = true

Or via environment variable:

export UNTOLD_METRICS=1
./YourApp

Enable periodic frame stats logging:

setEngineStatsLogging(
    enabled: true,
    profile: .compact,    // or .verbose
    intervalSeconds: 1.0
)

Read profiler snapshots programmatically:

let metrics = EngineProfiler.shared.snapshot()
print("CPU mean: \(metrics.cpuFrame.meanMs) ms")
print("GPU mean: \(metrics.gpuCommandBuffer.meanMs) ms")

let frameStats = getEngineStatsSnapshot()
print("Frame: \(frameStats.frameIndex)")
print("Update: \(frameStats.timing.updateMs) ms")
print("Render: \(frameStats.timing.renderTotalMs) ms")

OOC And Asset Triage Mode

High-volume instrumentation categories are disabled by default:

  • OOCTiming
  • OOCStatus
  • AssetLoader

Enable them when diagnosing OOC/loader behavior:

// Keep structured profiler metrics on
enableEngineMetrics = true
setEngineStatsLogging(enabled: true, profile: .compact, intervalSeconds: 1.0)

// Add focused trace logs
Logger.enable(category: .oocStatus)   // OutOfCore lifecycle/status
Logger.enable(category: .oocTiming)   // OOC timing detail
Logger.enable(category: .assetLoader) // progressive loader parse/upload

Disable after capture:

Logger.disable(category: .oocTiming)
Logger.disable(category: .oocStatus)
Logger.disable(category: .assetLoader)

Instruments Workflow

When metrics are enabled, the engine emits signpost scopes:

  • Frame
  • Update
  • RenderPrep
  • Encode
  • Submit

To inspect timeline data:

  1. Open Instruments
  2. Choose Points of Interest
  3. Filter subsystem to com.untoldengine.profiling
  4. Run the app with enableEngineMetrics = true (or UNTOLD_METRICS=1)

Build Configuration Notes

  • EngineProfiler is available in all configs, but disabled by default until enabled at runtime.
  • EngineStats collection is compiled in debug by default (ENGINE_STATS_ENABLED).
  • For release profiling with EngineStats, build with -DENGINE_STATS_ENABLED.

If ENGINE_STATS_ENABLED is not compiled in, getEngineStatsSnapshot() returns default values and setEngineStatsLogging(...) is effectively a no-op.

Category Toggle Notes

  • Category filtering applies to Logger.log(...) debug/info trace paths.
  • Warnings and errors still emit regardless of category state.
  • Logger messages are lazily evaluated, so disabled categories avoid message-building cost.

Debug Helper (DEBUG Only)

#if DEBUG
let metricsLogger = MetricsDebugLogger()
metricsLogger.logIfNeeded() // throttle-prints approximately once per second
#endif

Integrated Systems

Profiler hooks are already integrated into:

  • UntoldEngine.swift (runFrame)
  • RenderingSystem.swift (UpdateRenderingSystem)
  • UntoldEngineXR.swift (executeXRSystemPass)
  • UntoldEngineAR.swift (draw)