Unity performance (performance engineer)

Expert performance work is a measurement discipline: a budget in milliseconds, the bounding thread named before any change, the biggest measured cost fixed first, structure before tuning, and every fix proven with before/after numbers from a development player. An agent does all of it headless: AgentProfile in Editor Play mode to iterate, PerfProbe in a batch-mode player for verdicts, PerfCapture to attribute costs from a Profiler capture, metal_trace for GPU time, PerfBuild for size. Target: Unity 6000.3.21f1, URP 17.3, macOS Apple Silicon. If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.

REQUIRED BACKGROUND: scenario-unity-expert (channels, review loop, 6.3 traps, ut_* toolkit).

Stance (the expert delta)

1. Name the bound before touching anything. "If you speed up the GPU when your profile looks like this it's not going to run any faster" (Peter Hall, Unity Profiler team, _cV1B2hqXGI [00:05:50]). Observed: removing 1.36 MB of garbage per frame did not move a frame bound by 5,946 SetPass calls. GPU bound needs GPU timing; the Frame Debugger has none (Hall [frame 00:09:18]).
2. Players decide, the Editor iterates. The authority is a development build on the lowest target device (profiling e-book p. 18). GRD: 4.4x in a 2M-instance stress test, 2.07x in the Editor but 1.45x standalone in a real game (Oc6T4hh5gaI [frame 00:12:41]); here the Editor swung 1.5x to 3.0x, players 1.9x to 2.8x on a stress fixture. Forecast about 1.5x.
3. GC.Alloc sample time is not the cost. Unity records only timestamp and size (e-book p. 27): 54,021 allocations shown as 1.01 ms caused 19.97 ms of GC.Collect (Hall [frame 00:21:52]). Observed: 27,000 allocations per frame displayed 0.8 to 1.1 ms; the allocating code cost 3.8 to 5.4 ms. Count bytes and calls, measure collections, target 0 B per gameplay frame, and keep the probe itself allocation-free (git-amend ham_w48aRJ4 [00:11:30]).
4. 6.3 URP draw calls = SRP Batcher + GPU Resident Drawer; the 2024 advice is Built-in-only. Material "Enable GPU Instancing" off, static batching off, no MaterialPropertyBlock (6.3 Manual table). GRD silently does nothing unless BatchRendererGroup Variants = Keep All and every renderer of the URP asset is Forward+ or Deferred+ (URP 17.3 source, observed). Then prove coverage: GRD draws are named "Hybrid Batch Group" in the Frame Debugger (GUI editor only), each other draw is a renderer that fell out (MPB, LPPV, realtime GI, non-DOTS shader, skinned; 6.3 Manual); headless, check eligibility per renderer after Start.
5. Data layout first; spreading work over frames hides cost. 200,000 objects: MonoBehaviour Update 27 ms to 0.13 ms through manager, structs, Burst, SoA; "it's just spreading the work around" (Jason Booth, NAVbI1HIzCE [00:06:38]-[00:18:17]).
6. Attribute every hitch before fixing it, with markers kept in code. Streaming and spawn systems carry their own ProfilerMarkers and counters; Deep Profile only finds what fills a gap (Hall [00:18:39]-[00:19:12]). Compiles show as Shader.CreateGPUProgram (warm a traced GraphicsStateCollection during loading, Nicolas Borromeo CmD8MVGkDxQ [00:11:14]-[00:14:35]); here warm-up removed all 18 first-use compiles, yet the first frame stayed about 250 ms on Mono.JIT.
7. Resident memory kills, untracked usually does not. 0.75 GB untracked was 140 MB resident (Borromeo [00:32:22]); Editor memory is about 5x the player's (Uuzd39AjFWQ [00:10:03]). On a laptop, paging and VRAM overflow are stutter causes of their own.
8. Counts are exact, times drift [added, observed]. On a shared machine (load average 50 to 210 here), interleave A/B runs and require a consistent sign.

Establish first

Target platforms and min-spec device per tier; frame budget (16.67 ms desktop, mobile x 0.65); resolution and quality tier; what may change (code only, or art, design, feel); a repeatable benchmark, time-based when judging streaming (a fixed step per frame reaches boundaries sooner after a speed-up) [added]; scripting backend and build type; the machine actually measured (discrete GPU, on power; probe JSON device) [added]. Defaults: PC-tier URP asset, 60 fps, 1920x1080, development Mono player for iteration, IL2CPP release for size.

Workflow

1. Budget and benchmark. GATE: a baseline CSV.
2. Iterate in the Editor. ut_perf.profile (render=False isolates scripts), ab_profile for time deltas. GATE: numbers labeled "Editor, iteration".
3. Static baseline. PerfRendering.Audit (batching, GRD eligibility per renderer, graphics jobs per platform, Build Profile, stack traces, upload buffer, culling), lint_scripts, Project Auditor (project_auditor, Major first, triage_auditor keeps per-frame lines), PerfAudit.AudioImport, bundle_duplicates. GATE: findings triaged by call frequency.
4. Measure the player. build_player(development=True), run_player(..., shot=png, markers=[...]). GATE: draw_calls > 0, PNG opened, budget_check.
5. Classify the bound. Capture wait markers (capture_player, analyze_capture), longest vs median frame. GPU: metal_trace + metal_gpu_frames (GPU busy and per-pass ms; Rendering Debugger Display Stats in the GUI), then the pixel-bound test (4K vs 1080p, render scale). GATE: bound named with a number.
6. Attribute. attribute_spikes (your markers, GC.Collect, compiles, MeshCollider cooking, synchronous reads, physics steps), physics_catchup, memory_budget, density_check, allocations per block (AllocScope, Is.Not.AllocatingGCMemory()), GRD coverage (PerfFrameDebug.Capture or the window). GATE: top three costs named, no unexplained spike.
7. Fix one thing at a time, structure first. Scripts: allocations, managers, then Burst. Render CPU: Material Variants, SRP Batcher shaders, EnableGpuResidentDrawer, one camera, Split graphics jobs on DX12/Vulkan. GPU: dynamic resolution or STP, depth priming and less transparency, LOD where triangles are pixel-sized, post-processing on a fixed slice; shadows with scenario-unity-rendering-lighting. Hitches: async loads, prewarmed pools, PSO warm-up in loading, baked MeshColliders, audio load types, no duplicated bundle dependencies. GATE: compare_line shows the target down, nothing else up, image parity.
8. Ship config. IL2CPP release, stripping and code generation chosen, variants stripped against the used set (P15), flags through BuildPlayerOptions (platform profiles share settings). GATE: build succeeded, size explained, smoke run clean.
9. Guard. Allocation tests and Performance Testing sample groups per commit, lint on changed scripts. GATE: tests pass.

Numbers

Value	Relative to	Source
16.67 / 33.33 ms; x 0.65 mobile	frame budget at 60 / 30 fps; thermal headroom	profiling e-book p. 9, 36
0 B	managed allocation per gameplay frame	6.3 Manual; e-book p. 66
up to about 1 ms	per-frame cost of incremental GC write barriers	e-book p. 69
4.4x / 2.07x / 1.45x	GRD gain: 2M-instance stress / game in Editor / same game standalone	Oc6T4hh5gaI [frame 00:12:41]
217 / 199 / 176 / 161 fps	DX12 Split / Legacy / plain DX12 / Native graphics jobs	Oc6T4hh5gaI [frame 00:03:52]
256 vertices	below it GPU instancing is inefficient: combine instead	6.3 Manual
about 250 ms	one PSO creation stall	Oc6T4hh5gaI [frame 00:04:48]
4 pixel invocations	per one-pixel triangle (2x2 quads); gate 1 triangle per rendered pixel [added]	CmD8MVGkDxQ [00:27:26]
48.55 of 80 ms	per-frame Debug.Log in a development frame	xjsqv8nj0cw [00:10:23]
< 200 / > 400 KB	audio: Decompress On Load / Streaming	console e-book p. 104-105
up to 1 ms	CPU per extra active camera on mobile	console e-book p. 89
up to 10 s	startup added by Autoconnect Profiler	e-book p. 47
50% / 70% / 80% of RAM	memory budget: 2 GB phones / general / dedicated devices	Hall; Unity tutorial; e-book
5,946 to 33 SetPass; 58-60 to 5.2-6.2 ms	3,000 spheres, MPB tint to 8 Material Variants, dev player	observed
18 to 0	first-use Shader.CreateGPUProgram after warming 10 PSOs (3.6 ms at load)	observed
177.9 / 110.5 / 116.3 MB	macOS app: IL2CPP Minimal + speed / IL2CPP High + size / Mono	observed
14.75 M to 0.26 M triangles (7.1 to 0.12 per pixel)	400 dense meshes after Mesh LOD, draw calls unchanged	observed
57.1 ms frame = Spawn.Burst 26.9 ms + 4 compiles; next frame 3 physics steps	burst of 3,000 Instantiate read through its own marker	observed
48-80 ms vs 0 ms	MeshCollider cooking at spawn vs Physics.BakeMesh in a job at load (40 meshes)	observed
33 us vs 2.6-3.9 us	per Debug.Log, stack traces ScriptOnly vs None (dev player)	observed
2.5 vs 5.8 ms; 1.2x at 4x pixels	GPU busy vs CPU main (Metal System Trace); 4K vs 1080p: not pixel bound	observed
1,944 to 1,002 KB	two bundles sharing a texture: implicit copies vs a shared bundle	observed

Quality gates

• Measurable: player budget_check pass (p95 under budget, no gameplay hitch); gc_check pass in the player; attribute_spikes unexplained = 0; physics_steps at most 1 outside a forced spike; memory_budget pass; density_check pass; PerfRendering.Audit counts.error == 0 and every GRD fallout explained; 0 Shader.CreateGPUProgram after loading; no new Major Project Auditor issue in your code; IL2CPP build within budget.
• Visual: the player's last frame (-perfShot) and Editor captures from the same bookmarks before and after, ut_review.compare, contact sheet opened; no blank, uniform or magenta frame.

Common mistakes

Mistake	What it looks like	Fix
Optimizing the side that is not bound	fewer allocations, same frame time	classify first (wait markers, GPU busy, SetPass)
Trusting Editor numbers or one run	"3x faster" gone in the player	player CSV; ab_profile with consistent sign
Benchmarking a batch-mode player that renders nothing	0.3 ms frames, 0 draw calls	PerfProbe submit + -perfShot
GRD on, nothing changes	draw calls unchanged	Keep All, Forward+/Deferred+, static batching off, fallouts fixed
MaterialPropertyBlock for per-object color	SetPass = draw calls; StdRender.ApplyShader dominates	Material Variants; unity_RendererUserValue with GRD
Reading GC.Alloc ms as the cost	"allocations cost 0.5 ms"	count and bytes, GC.Collect ms, A/B
A monitor that formats strings each frame	GC column never 0	preallocated buffers, write once (PerfProbe)
Closure in a rarely taken branch	allocations with the feature off	move captured locals into the branch
Deep Profile to find a spike	inflated small functions	markers and counters kept in code, -perfMarkers
GPU tuned from the Frame Debugger	guessed timings	metal_trace (PIX, Nsight on Windows)
Fixed render scale on a laptop	fine cold, hitches when hot or loaded	dynamic resolution; STP at a fixed scale only for a fixed pixel bound
Warm-up assumed to fix a first-frame hitch	still 250 ms	capture: JIT means IL2CPP, loading means async
Frame-spreading as the fix	lower peak, same total	measure unamortized first, fix structure
MeshCollider added at runtime	spawn spike, Physics.BakePhysXCollisionMeshData	Physics.BakeMesh in a job, Prebake Collision Meshes
Development flag set through EditorUserBuildSettings	every platform profile changed	BuildPlayerOptions or a build profile asset
Sizing from BuildReport totalSize	1.9 GB for a 178 MB app	shipped folder on disk
InstantiateAsync as a hitch fix	17 to 83 ms frame later	pool and prewarm behind a transition
Benchmarking the first launch of a new build	212 vs 22 ms	discard the first launch

What not to change without sign-off

Game feel (fixed timestep, Maximum Allowed Timestep, animation timing, input, AI ticks); art direction (texture sizes, lights, LOD thresholds, render scale) without before/after captures; the pipeline, engine version or an ECS rewrite; incremental GC off unless gameplay allocates 0 B in the player and an A/B shows the gain; asyncUploadBufferSize raised blindly (never returned, console e-book p. 31); VSync off in release; the benchmark path between before and after.

Handoffs

• Receives: the brief in numbers from scenario-unity-expert; systems code from scenario-unity-architecture and scenario-unity-gameplay; pipeline assets from scenario-unity-rendering-lighting; shaders from scenario-unity-shaders; effects from scenario-unity-vfx; UI from scenario-unity-ui; bundles and Addressables from scenario-unity-pipeline-automation.
• Delivers: the bound, attributed costs, before/after tables, CSVs, traces, PNGs: variant stripping to scenario-unity-shaders, lighting, shadow and post cuts to scenario-unity-rendering-lighting, overdraw budgets to scenario-unity-vfx and scenario-unity-ui, physics settings to scenario-unity-gameplay, duplicate fixes, CI perf tests and build profiles to scenario-unity-pipeline-automation, device and thermal validation to scenario-unity-mobile, Web limits to scenario-unity-web.

Unity 6.3 notes

• SRP Batcher + GRD + GPU occlusion (the 17.3 URP asset holds the occlusion flag); dynamic batching deprecated in 6.5, obsolete in 6.6.
• Split graphics jobs is the default on DX12/Vulkan/consoles (Oc6T4hh5gaI [00:03:04]); the 6.3 URP template reads Windows on/Split, Android off/Native, Metal off/Native; per-platform getters are internal (observed).
• GraphicsStateCollection is experimental, traces only in development players; WebGPU tracing in 6.4. FrameDebuggerUtility is internal.
• Profile Analyzer 1.4.0, Memory Profiler 1.1.12, Project Auditor 1.0.2 (built in from 6.4), Performance Testing 3.5.0 (core in 6.6) and Profiling Core 1.0.3 (needed for ProfilerCounterValue) are preinstalled packages added by name.
• Mesh LOD is 6.2+. Physics.BakeMesh(int, bool) is obsolete: pass mesh.GetEntityId(). 6.3 runs Boehm (non-generational); CoreCLR is future work.

References

• references/procedures.md: eighteen procedures with full calls, each with its live test and recorded result.
• references/expert-notes.md: principles by expert with timestamps, disagreements and deciding conditions.
• references/critique.md: the rubric for judging a performance pass.
• references/gui-paths.md: Profiler, Frame Debugger, Rendering Debugger, Project Auditor and settings paths.
• references/sources.md: every source with credentials, URLs, best timestamps and revision history.
• scripts/ut_perf.py (runner side), scripts/AgentKit/Performance/*.cs (Editor jobs), scripts/Runtime/Performance/*.cs (PerfProbe, AllocScope).