Mobile graphics optimization guides for Unity users

1. Confidential © 2018 Arm Limited
Owen Wu (owen.wu@arm.com)
Developer Relations Engineer
Mobile Graphics
Optimization
Guides

2. Confidential © 2018 Arm Limited
Who We Are
Arm Developer Relations Introduction

3. 3 Confidential © 2018 Arm Limited
Who We Are
• Arm provides CPU & GPU IPs to Silicon Vendor
• We don’t make chips
• Clients including Apple, Samsung, Nintendo, Qualcomm, MediaTek, etc.
• Softbank acquired us in 2016
• >95% market share of smartphone CPU
• >1 Billion GPU shipped in 2018
• We help developers to make better game

4. 4 Confidential © 2018 Arm Limited
What We Can Help
• Developer education
• Game issue investigation
• Game performance analysis
• Game performance optimization
• Deep collaboration for Mali GPU
• Game promotion on Arm/Partner global events
• Development devices (in the future)

5. Confidential © 2018 Arm Limited
Optimization
Guides

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Why Optimize
with reliable performance, smooth
gameplay, and long battery life
Retain users
by ensuring good user experience on a
wide range of consumer devices
Widen market
by maximizing rendering effectiveness inside
a 2.5 Watt system-wide power budget
Enhance visuals

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Best Parctices of Optimization
• Write code with optimization in mind
• Hardware knowledge
• Check performance regression everyday
• Arm Performance Advisor
• Don’t do deep optimization too early
• Arm Mobile Studio

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How To Do Optimization
• Knowledge of hardware
• Gather reliable and stable data
• Identify bottleneck first
• Find out why bottleneck happened
• Figure out the solution
• Verify the solution
• Optimize one thing at one time

9. Confidential © 2018 Arm Limited
Basic Hardware
Concepts

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Pipeline Stages
Application
Graphics
Driver
Vertex
Shader
Primitive
Assembler
Rasterizer
Early Frag
Op
Fragment
Shader
Late Frag OpBlending
Color
Output
Depth
Output
Stencil
Output

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GPU Is Multi-threading
• Traditional API is single threaded
• Driver hides the complexity
• CPU and GPU is running parallelly
• Every tasks in GPU are running parallelly too
• Optimization goal – keep GPU as busy as possible

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GPU
Desktop GPU – Immidate Rendering Mode
Vertex Shader
Fragment
Shader
Frame Buffer 0Frame Buffer 1
Application Draw Calls

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Mobile GPU – Tiled Rendering Mode
GPU
Vertex Shader
Fragment
Shader
Frame Buffer 0Frame Buffer 1
Application Draw Calls

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External Memory / Memory Bandwidth
• Mobile’s external memory bandwidth is much smaller than
desktop’s
• Read or write to external memory is very power consuming
• Tile based rendering mode reduce the memory bandwidth
requirement
• GPU computing power advances faster than memory bandwidth
• Usually 2GB/s is recommended
GPU
Tile
Memory
External memory
Slow Path

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Cache
• Keep data in fast memory
• Cache size is small
• Keep data small so cache can keep more data
• Sequential access can increase cache hit rate

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Pixel/Fragment/Texel
• Pixel is a single position data on frame buffer
• Fragment is a thread in GPU which will output a pixel
• Texel is a single position data on texture

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Texture Compression
• ASTC may get better quality with same memory size as ETC.
• Or same quality with less memory size than ETC.
• ASTC takes longer to encode compared to ETC and might make the game packaging
process take longer time. Due to this, it is better to use it on final packaging of the
game.
• ASTC allows more control in terms of quality by allowing to set block size. There are no
single best default in block size, but generally setting it to 5x5 or 6x6 is good default.

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Texture Color Space
• Use linear color space rendering if using lighting
• Check sRGB in texture inspector window
• Textures that are not processed as color should NOT
be used in sRGB color space (such as metallic,
roughness, normal map, etc).
• Current hardware supports sRGB format and
hardware will do Gamma correction automatically for
free

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Texture Filtering
• Trilinear - Like Bilinear but with added blur
between mipmap level
• Don’t use trilinear with no mipmap
• This filtering will remove noticeable change
between mipmap by adding smooth transition.

20. 20 Confidential © 2018 Arm Limited
Texture Filtering
• Anisotropic - Make textures look better when
viewed from different angle, which is good for
ground level textures
• Higher anisotropic level cost higher

21. 21 Confidential © 2018 Arm Limited
Texture Filtering
• Use bilinear for balance between performance and visual quality
• Trilinear will cost more memory bandwidth than bilinear and needs to be used
selectively
• Bilinear + 2x Anisotropic most of the time will look and perform better than Trilinear +
1x Anisotropic, so this combination can be better solution rather than using Trilinear.
• Keep the anisotropic level low. Using a level higher than 2 should be done very
selectively for critical game assets.
• This is because higher anisotropic level will cost a lot more bandwidth and will affect device battery life.

22. Confidential © 2018 Arm Limited
Best Optimization
Practices of Mali
GPU

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Reduce Render State Switch
• Render state switch is very expensive operation
• Rendering as many primitives as possible in one draw call
• Don’t just check number of draw calls or batches
• Number of render state switch is also an important index
• Using Tris/SetPass (i.e. 95.2K/34) is more accurate
• Batch as many draw call as possible
• Static batch
• GPU Instancing
• Dynamic batch

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Reduce Frame Buffer Switch
• Bind each frame buffer object only once
• Making all required draw calls before switching to the
next
• Avoid unnecessary context switch
• Use Unity frame debugger to check
• Use Arm Mobile Studio to do API level check

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Clear Frame Buffer Before Rendering
• Before rendering, GPU will read frame buffer into tile
memory from external memory
• Minimizing start of tile loads
• Can cheaply initialize the tile memory to a clear color value
• Ensure that you clear or invalidate all of your attachments at
the start of each render pass
• Use Unity frame debugger to check
• Use Arm Mobile Studio to do API level check
No clear before
switching render target.
Bad for performance.

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Reduce Frame Buffer Write
• After rendering, GPU will write result to external
memory from tile memory
• Minimizing end of tile stores
• Avoid writing back to external memory whenever is
possible
• Disable writing to depth/stencil buffer if
depth/stencil value is not used
• Use Unity frame debugger to check
• Use Arm Mobile Studio to do API level check

27. 27 Confidential © 2018 Arm Limited
Avoid Rendering Small Triangles
• The bandwidth and processing cost of a vertex is typically orders
of magnitude higher than the cost of processing a fragment
• Make sure that you get many pixels worth of fragment work for
each primitive
• Make sure each model which create at least 10-20 fragments
per primitive
• Use dynamic mesh level-of-detail, using simpler meshes when
objects are further away from the camera

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Take Advantage of Early-Z
• Many fragments are occluded by other fragments
• Running fragment shader of occluded fragment is wasting GPU
power
• Render opaque object from front to back
• Occluded fragment will be rejected if
• Fragment shader doesn’t use discard
• Fragment shader doesn’t write value to depth buffer
• Alpha-to-coverage is OFF
• Otherwise the fragment will go Late-Z path which rejects
occluded fragment after fragment shader
Early Frag
Op
Fragment
Shader
Late Frag Op

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Always Use Mipmap If Camera Is Not Still
• Using mipmapping will improve GPU performance
• Less cache miss
• Mipmapping also reduce texture aliasing and improve final image
quality

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Don't Use Pre-Z Pass
• The opaque geometry is drawn twice, first as a depth-only update, and then as a color render which uses
an EQUALS depth test to reduce the redundant fragment processing
• Mali GPU has already include optimizations such as FPK to reduce the redundant fragment processing
automatically
• The cost of the additional draw calls, vertex shading, and memory bandwidth nearly always outweighs
the benefits of Z-prepass

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Shader Floating-point Precision
• Use mediump and highp keywords
• Full FP32 of vertex attributes is unnecessary for many uses of attribute data
• Keep the data at the minimum precision needed to produce an acceptable final output
• Use FP32 for computing vertex positions only
• Use the lowest possible precision for other attributes
• Don’t always use FP32 for everything
• Don’t upload FP32 data into a buffer and then read it as a mediump attribute

32. Confidential © 2018 Arm Limited
Arm
Mobile Studio
Introduction

33. 33 Confidential © 2018 Arm Limited
What is in the box?
Streamline
Graphics
Analyzer
Mali Offline
Compiler
(separate download)
Performance
Advisor
(closed beta)
Download Arm Mobile Studio: http://developer.arm.com/mobile-studio

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Streamline
Performance Analyzer
Mali GPU support
 Analyze and optimize Mali™ GPU
graphics and compute workloads
 Accelerate your workflow using
built-in analysis templates
Optimize for energy
 Move beyond simple frame time
and FPS tracking
 Monitor overall usage of processor
cycles and memory bandwidth
Speed up your app
 Find out where the system is
spending the most time
 Tune code for cache efficiency
Application event traceNative code profiling
 Break performance
down by function
 View cost alongside
disassembly listing
Arm CPU support
 Profile 32-bit and 64-bit apps for
ARMv7-A and ARMv8-A cores
 Tune multi-threading for
DynamIQ multi-core systems
 Annotate software
workloads
 Define logical event
channel structure
 Trace cross-channel
task dependencies
Tune your rendering
 Identify critical-path GPU
shader core resources
 Detect content inefficiency

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Streamline

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Triage nurse scenarios
Vsync bound Fragment bound CPU bound
Serialization problems Thermally bound
16.6 ms

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Graphics Analyzer
GPU API Debugger
Shader analysis
 Capture and view all shaders used
 Optimize shader performance using
integrated Mali Offline Compiler
Cross platform
 Host support for Windows,
macOS, and Linux
 Target support for any Android
GPU
Rendering API debug
 Graphics debug for content
developers
 Support for all versions of
OpenGL ES and Vulkan
Android utility appVisual analysis views
 Native mode
 Overdraw mode
 Shader map mode
 Fragment count mode
State visibility
 Show API state after every API call
 Trace backwards from point-of-use
to API call responsible for state set
 Manage on-device
connection
 Select and launch
user application
Frame analysis
 Diagnose root causes
of rendering errors
 Identify sources of
rendering inefficiency

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Trace outline
Frame capture
Vertex data
API calls
Statistics
Target state
Shaders
Textures,
Buffers,
Uniforms,
…

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s
Mali Offline Compiler
Shader static analysis
Rapid iteration
 Verify impact of shader changes
without needing whole application
rebuild
Profile for any Mali GPU
 Cost shader code for every Mali
GPU without needing hardware
Mali GPU aware
 Support for all actively
shipping Mali GPUs
 Cycle counts reflect
specific microarchitecture
Critical path analysisControl flow aware
 Best case control flow
 Worst case control flow
Syntax verification
 Verify correctness of code changes
 Receive clear error diagnostics for
invalid shaders
 Identify dominant
shader resource
 Target this for
optimization!
Register usage
 Work registers
 Uniform registers
 Stack spilling

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Mali Offline Compiler
 Use GA to capture the API calls and shaders to
understand the AP behavior.
 Use Offline Shader compiler to profiling
instruction counts for ALU, L/S, TEX
 If the shader needs more registers than the
available one, the GPU would need to perform
registers spilling
 registers spilling will cause big inefficiencies
and higher Load/Store utilization
Mali_Offline_Compiler_v4.3.0$ ./malisc --core Mali-T600 --revision
0p0_15dev0
--driver Mali-T600_r4p0-00rel0 --vertex shader-176.vert –V
ARM Mali Offline Shader Compiler v4.3.0 (C) Copyright 2007-2014
ARM Limited. All rights reserved.
Compilation successful. 3 work registers used, 16 uniform registers
used, spilling not used.
A L/S T Total Bound
Cycles: 9 5 0 14 A
Shortest Path: 4.5 5 0 9.5 L/S
Longest Path: 4.5 5 0 9.5 L/S
Note: The cycles counts do not include possible stalls due to cache
misses.

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Performance Advisor
Analysis Reports
Fast workflow
 Integrate data capture and analysis
into nightly CI test workflow
 Read results over a nice cup of tea
Caveats …
 Still under development
 Currently in closed beta
Overview chartsRegion views
 Split by dynamic
behavior
 Split by application
annotation
Executive dashboard
 Show high level status summary
 Show status breakdown by regions
of interest
 See performance
trends over time
 See region splits
Summary reports
 Easy-to-use performance
status reports
 Integrated initial root cause
analysis

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Performance Advisor
• An automated performance triage nurse
• Move beyond simple FPS-based regression tracking
• Perform an automated first pass analysis
• Generate easy to read performance report
• Route common issues directly to the team to review
• Free up performance experts to focus on the difficult problems
• Integrate into nightly continuous integration
• Catch major issues early
• Detect gradual regressions before they start impacting users

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Region-by-region analysis

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Thank You
Danke
Merci
谢谢
ありがとう
Gracias
Kiitos
감사합니다
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Confidential © 2018 Arm Limited

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Confidential © 2018 Arm Limited