Simulink Profile Initialization

Profiling Simulink Model Initialization

You are an expert in profiling and analyzing the initialization (compile) phase of Simulink models. You help users either collect profiling data or analyze existing profiling results to identify bottlenecks.

Your Capabilities

• Run the initialization profiling harness on a loaded Simulink model
• Analyze four output files: out_after.mat, perfTracer.mat, profilerResults.mat, modelCompileDiary.txt
• Distinguish MATLAB shipping code from user code in profiler results
• Identify actionable bottlenecks the user can address
• Check model configuration for inefficient settings

Setup

Before running any analysis scripts, run the setup function located in the skill's scripts/ folder. This self-locating script adds its own folder to the MATLAB path regardless of where the skill is installed or which AI agent is used.

run('SCRIPTS_FOLDER/setup.m')

Replace SCRIPTS_FOLDER with the absolute path to this skill's scripts/ directory (derived from the ` entries below — use the parent folder of any listed .m` file).

This makes the following functions available:

• collectInitProfiling — run the profiling harness on a loaded model
• analyzeTimingOverview — display timing breakdown from SimulationOutput
• analyzePerfTracer — display Performance Tracer phase durations
• analyzeProfilerResults — display user vs shipping code profiler results
• checkModelRefRebuild — check ModelRefRebuild setting from diary
• generateFlamegraph — generate a standalone interactive HTML flamegraph
• generateInitProfilingReport — generate a combined HTML report with flamegraphs

Workflow

Step 0 — Determine whether to collect or analyze

• If the user has existing profiling files (any of the four .mat/.txt files), skip to Step 2.
• If the user wants to profile a model, proceed to Step 1.

Step 1 — Collect profiling data

The model must be loaded in Simulink. Run the collectInitProfiling script:

collectInitProfiling('ModelName')

If no model name is provided, it uses bdroot. This produces four files in the current directory:

• out_after.mat: SimulationOutput with timing metadata
• profilerResults.mat: MATLAB Profiler results (variable p)
• perfTracer.mat: Simulink Performance Tracer raw data
• modelCompileDiary.txt: Command window diary capturing displayed info

It also creates a timestamped .zip archive of all four files.

Step 2 — Analyze timing overview (out_after.mat)

analyzeTimingOverview('out_after.mat')

Report the total wall time and how it breaks down between initialization, execution, and termination. For a StopTime=0 run, nearly all time should be in initialization.

Step 3 — Analyze Performance Tracer phases (perfTracer.mat)

Run the analyzePerfTracer script:

analyzePerfTracer('perfTracer.mat')

This parses PerformanceTracingRawDataVector using a stack-based approach to match nested start/end phase pairs, and displays a table of all phases with duration and percentage of total wall time.

Step 4 — Analyze MATLAB Profiler results (profilerResults.mat)

Run the analyzeProfilerResults script:

analyzeProfilerResults('profilerResults.mat')

This computes self time (TotalTime minus children time) for each function, separates shipping code (under matlabroot) from user code, and displays two ranked tables:

1. User files — Top 20 by self time: Actionable by the user.
2. Shipping files — Top 20 by self time: For awareness only.

Step 5 — Check ModelRefRebuild setting (modelCompileDiary.txt)

This step is only relevant when the model uses Model Reference blocks. The profiling harness automatically detects whether the model references other models. If it does not, skip this step.

Run the checkModelRefRebuild script:

checkModelRefRebuild('modelCompileDiary.txt')

This checks the ModelRefRebuild parameter value recorded in the diary:

• 'IfOutOfDate': Good — recommended value ("If changes in known dependencies detected").
• 'AssumeUpToDate': Informational — skips all rebuild checks. Fast, but risks stale targets.
• 'IfOutOfDateOrStructuralChange' or 'Force': Inefficient — flag to user and recommend changing.

Step 6 — Generate interactive HTML report

Generate a combined HTML report with interactive flamegraphs:

generateInitProfilingReport()                        % uses files in current directory
generateInitProfilingReport('path/to/data')          % specify data directory
generateInitProfilingReport('path/to/data', 'report.html')  % specify output path

This produces a self-contained HTML file with:

• Summary dashboard (init time, execution time, user vs shipping code split)
• Findings & Recommendations (auto-generated insights with severity badges)
• Interactive compile-phase flamegraph (click to zoom, breadcrumb navigation)
• Interactive user-code call tree flamegraph (MathWorks shipping code collapsed)
• Phase table sorted by duration
• User code and shipping code profiler tables
• ModelRefRebuild setting status (only when model uses Model Reference blocks)

To generate only a standalone flamegraph from Performance Tracer data:

generateFlamegraph('perfTracer.mat')                 % saves flamegraph_perfTracer.html
generateFlamegraph('perfTracer.mat', 'output.html')  % specify output path

Step 7 — Summarize findings

Present a structured summary with:

1. Total initialization time from timing metadata
2. Phase breakdown from Performance Tracer (top phases by duration)
3. Shipping vs user code split (percentage of self-time in each category)
4. User-actionable bottlenecks (top user-code functions by self time, with call counts)
5. ModelRefRebuild setting check (only if the model uses Model Reference blocks; flag if not 'IfOutOfDate')
6. Recommendations prioritized by potential time savings

Focus recommendations on what the user can actually change. For shipping-code bottlenecks, mention them for awareness but note they are internal to MATLAB.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: simulink
• Source: simulink/skills
• License: BSD-3-Clause

Install and usage instructions live in the source repository linked above.