Cell today and tomorrow

1. Systems and Technology Group
© 2005 IBM Corporation
Cell today and tomorrow
H. Peter Hofstee, Ph. D.
Cell Chief Scientist and
Chief Architect, Cell Synergistic Processor
IBM Systems and Technology Group
SCEI/Sony Toshiba IBM (STI) Design Center
Austin, Texas

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Acknowledgements
ƒ Cell Broadband Engine (“Cell”) is the result of a deep
partnership between SCEI/Sony, Toshiba, and IBM
ƒ Cell represents the work of more than 400 people
starting in 2001and a design investment of about
$400M

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Agenda
ƒ Basics
– Performance: Power wall , Memory/Latency wall
– Multicore and specialization
ƒ Cell
– Asynchronous load/store (DMA)
– Microarchitecture decisions
ƒ Cell Performance
– Things that work really well
– Things that will likely work well
– Question marks
ƒ Cell Systems
ƒ Future of Cell and things for Academia to look at

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BASICS

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Computing Paradigm Shift
Today:
– Single thread performance hitting limits
• Architecture and process technology saturated
• Small percentage gains expected to remain
But:
– Signs of paradigm shift to application
specific system customization
• Large multiple gains for specific applications
• Cell
–~50x on TRE, ~100x on FFT
• Datapower
–XML acceleration
• Many examples in embedded markets
Future:
– Greater performance demands
• Immersive Interaction
–3D, real-time, gaming inspired applications
–Rich media, data-intensive content
• Sensory Computing
–New network tier
–Autonomous agents performing intelligent analysis on streaming data
>A&D: battlefield coordination
Single Thread Performance
SPECint
Single thread
performance
growth rate slows
dramatically
Historical Trend
45% CGR

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Solutions
ƒ Memory wall:
– More slower threads
– Asynchronous loads
ƒ Efficiency wall:
– More slower threads
– Specialized function
ƒ Power wall:
– Reduce transistor power
• operating voltage
• limit oxide thickness scaling
• limit channel length
– Reduce switching per function
INCREASE
CONCURRENCY:
Multi-Core
INCREASE
SPECIALIZATION:
Non-Homogeneous

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CELL

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Motivation: Cell Goals
ƒ Outstanding performance, especially on
game/multimedia applications.
– Challenges: Power Wall, Frequency Wall, Memory Wall
ƒ Real time responsiveness to the user and the
network.
– Challenges: Real-time in an SMP environment, Security
ƒ Applicable to a wide range of platforms.
– Challenge: Maintain programmability while increasing performance
ƒ Support an introduction in 2005/6.
– Challenge: Structure innovation such that 5yr. schedule can be met

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Cell Concept
ƒ Compatibility with 64b Power Architecture™
– Builds on and leverages IBM investment and community
ƒ Increased efficiency and performance
– Non Homogenous Coherent Chip Multiprocessor
• Allows an attack on the “Frequency Wall”
– Streaming DMA architecture attacks “Memory Wall”
– High design frequency, low operating voltage attacks “Power Wall”
– Highly optimized implementation
ƒ Interface between user and networked world
– Flexibility and security
– Multi-OS support, including RTOS/non-RTOS
– Architectural extensions for real-time management

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Cell Architecture is …
COHERENT BUS
Power
ISA
MMU/BIU
Power
ISA
MMU/BIU
…
IO
transl.
Memory
Incl. coherence/memory
compatible with 32/64b Power Arch. Applications and OS’s
64b Power Architecture™

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Cell Architecture is … 64b Power Architecture™
COHERENT BUS (+RAG)
Power
ISA
+RMT
MMU/BIU
+RMT
Power
ISA
+RMT
MMU/BIU
+RMT
IO
transl.
Memory
Plus
Memory
Flow Control (MFC)
MMU/DMA
+RMT
Local Store
Memory
MMU/DMA
+RMT
Local Store
Memory
LS Alias
LS Alias
…
…
…

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Cell Architecture is … 64b Power Architecture™+ MFC
COHERENT BUS (+RAG)
Power
ISA
+RMT
MMU/BIU
+RMT
Power
ISA
+RMT
MMU/BIU
+RMT
IO
transl.
Memory
Plus
Synergistic
Processors
MMU/DMA
+RMT
Local Store
Memory
MMU/DMA
+RMT
Local Store
Memory
LS Alias
LS Alias
…
…
…
Syn.
Proc.
ISA
Syn.
Proc.
ISA

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Asynchronous Load/Store (DMA)
ƒ THE major architectural decision in Cell
– Motivated by memory wall
– Enabled by a large market
ƒ Fundamental change to programmers.
– Transition from demand-fetch to software controlled
prefetch
– Bill Dally’s “plumbing project analogy”
– “Bucket brigade” analogy

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Permute Unit
Load-Store Unit
Floating-Point Unit
Fixed-Point Unit
Branch Unit
Channel Unit
Result Forwarding and Staging
Register File
Local Store
(256kB)
Single Port SRAM
128B Read 128B Write
DMA Unit
Instruction Issue Unit / Instruction Line Buffer
8 Byte/Cycle 16 Byte/Cycle 128 Byte/Cycle
64 Byte/Cycle
On-Chip Coherent Bus
SPE BLOCK DIAGRAM

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Other (Micro)Architectural and Decisions
ƒ Large shared register file
ƒ Local store size tradeoffs
ƒ Dual issue, In order
ƒ Software branch prediction
ƒ Channels
Microarchitecture decisions, more so than architecture decisions
show bias towards compute-intensive codes

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First pass hardware measurement in the
Lab - Nominal Voltage = 1V
0.9 1 1.1 1.2
Supply Voltage
3
3.5
4
4.5
Frequency
[GHz]
Fmax
Hardware Performance Measurement
(85°C)
ƒ 250M transistors … 235mm2
ƒ Top frequency >4GHz
– Lab conditions
– Most efficient at ~1V
ƒ > 200 GFlops (SP) @3.2GHz
ƒ > 20 GFlops (DP) @3.2GHz
ƒ Up to 25.6 GB/s memory B/W
ƒ Up to 70+ GB/s I/O B/W
– Practical ~ 50GB/s
ƒ 100+ simultaneous bus
transactions
– 16+8 entry DMA queue per SPE
CELL PROCESSOR STATISTICS

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CELL PERFORMANCE
(AND PROGRAMMING)

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Things that work extremely well today ( up to 100x)
ƒ Problem can be re-coded
ƒ Predictable non-trivial memory access pattern
– Can build scatter-gather lists
ƒ Problem can benefit from SIMD
ƒ Focus on 32b float, or <=32b integer
ƒ Examples:
– FFTw ( best result about 100GFlops )
– Terrain Rendering Engine
– Volume rendering
ƒ Typical code is double-buffered gather-compute-scatter

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Things that work well today ( about 10-20x)
ƒ Compute bound codes
ƒ Small enough to be rewritten
ƒ Main datatype is 32b float or <= 32b Int
ƒ Benefits from SIMD
ƒ Examples:
– Crypto codes ( RSA, SHA, DES, etc. etc. etc.)
– Media codes ( MPEG 2, MPEG 4, H.264, JPEG )
– … many many others …

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Things likely to work well
ƒ Library .. Device/API based applications
– Graphics and physics and sound and …
ƒ Scientific codes … library based
– No rewrite
– If granularity is ok

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Question marks
ƒ Can a compiler based approach, without restructuring code
specifically for the SPEs result in a chip-level advantage?
– About 3-4x more SPEs in same area or power
– But, have to compiler manage local store
ƒ Interesting benchmarks: SpecFP, MediaBench, EEMBC, etc.
– New more explicitly parallel benchmarks?
ƒ Would you ever use an SPE for a SpecInt-type workload?

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Cell based systems

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Cell Processor Isn't Just for Games.
Innovative Chip is best high-performance embedded processor of 2005
We chose the Cell BE as the best high-performance embedded processor of 2005 because of its
innovative design and future potential....Even if the Cell BE accumulates no more design wins, the
PlayStation 3 could drive sales to nearly 100 million units over the likely five-year lifespan of the
console. That would make the Cell BE one of the most successful microprocessors in history.
“…Cell could power
hundreds of new apps,
create a new video-
processing industry and
fuel a multibillion-dollar
build out of tech hardware
over ten years.”
-- Forbes
“It was originally conceived
as the microprocessor to
power Sony's [PS3], but it is
expected to find a home in
lots of other broadband-
connected consumer items
and in servers too.”
-- IEEE Spectrum

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Cell BE based Systems: SCEI, Mercury, … and IBM!

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ƒ Toshiba Announces Cell Chip Set and Cell Reference Set
20 September, 2005
ƒ Tokyo--Toshiba Corporation today took major steps toward creating a comprehensive development environment for applications based on the Cell
microprocessor with the announcement of a Cell Chip Set consisting of the new microprocessor and key peripheral chips, and a Cell Reference Set
development platform. The chip set and the reference set will support development of digital consumer products and communication equipment that
draw on the powerful broadband capabilities of the Cell microprocessor.
ƒ "Software developers and other customers will be eager to make full use of Cell's unsurpassed multitasking and real-time processing functions," said
Tomotaka Saito, General Manager of Broadband System LSI Division, Toshiba Corporation Semiconductor Company. "The Cell Chip Set and Reference
Set will support them in developing products and applications that reach new levels of performance and excitement."
ƒ The Cell Chip Set is composed of the Cell processor, a Super Companion Chip—the interface between Cell and external audio/visual input/output
equipment—and a power supply system chip optimized to drive the Cell microprocessor.
ƒ The Cell Reference Set development platform consists of a Cell microprocessor, peripheral chips mounted on a printed circuit board with a general-use
interface, peripheral equipment, such as DVD and HDD drives, and cooling equipment required for stable operation, all housed in case. The available
software includes operating systems and middleware and software development tools. This combination of hardware and software reduces
development costs, cuts turnaround time and simplifies testing.
ƒ Toshiba expects to start marketing the chips set and reference set in April 2006 or later, once it has assured supply of the component chips and all
related documentation.
ƒ Toshiba Corporation will showcase the Cell Chip Set and Cell Reference Set, and demonstrate digital media applications on the Cell Reference Set at
the Toshiba booth of CEATEC JAPAN 2005, from October 4 to October 8 at Makuhari Messe.
ƒ Outlines of Cell Chip Set and Cell Reference Set:
ƒ Cell Chip Set:
ƒ Cell microprocessor: Next generation microprocessor jointly developed by IBM, Sony Group and Toshiba. Adopts a multi-core architecture and offers
super high-speed data transfer capability. The processor is expected to find application in equipment handling data-rich media applications.
ƒ Super Companion Chip: Cell's peripheral LSI, which houses audio and image interfaces supporting Cell's super high-speed data transfer capability.
The chip also supports a group of interfaces for various systems (video, audio input/output, digital AV interface, IEEE1394, digital tuner interface) and a
group of interfaces that make it easier to connect standard input/output devices (standard bus interface, high speed network interface and storage
device interface.)
ƒ Highly efficient power supply system: The supply system is optimized to drive the Cell processor. Includes controller LSI, TB6814FLG, which makes it
possible to offer high-speed response and high-accuracy required by Cell. Includes multi-chip module, TB7003FL, which embeds power device in a
small 8mm x 8mm package. Realizes small, high-power and high-efficient power supply system which has 4 phases of 1MHz high-speed switches.
ƒ Cell Reference Set:
ƒ Development platform for Cell-based, next generation digital consumer products,
ƒ High-speed multi-bit wiring technology and wide variety of interfaces that supports broadband system architecture
ƒ Linux and ITRON are both provided on the hypervisor OS that manages hardware resources. This approach facilitates the reuse of application property.
ƒ A comprehensive development environment including the Eclipse framework based editor, compiler, debugger, and performance monitor.
ƒ An audio-visual application model includes simultaneous multiple digital and analog broadcast television reception, recording and playback.
SOURCE: TOSHIBA

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Future of Cell and
Things for Academia to look at

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User Interaction Drives Innovation in Computing
Time
Punch Cards
Green Screen/
Teletype
Spreadsheet
WWW
Gaming
Main Frame
Multitasking
Main Frame
Batch
Client/Server
Internet
Mini-Computer
WYSIWYG
Stand Alone PC
Windows
Word
Processing
Level
of
Interaction
Immersive Interaction
Online Gaming
Source: J.A. Kahle

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Characteristics of the Latest Transition in User Interaction
ƒ Windows
ƒ Click and wait…
ƒ Client-centric
ƒ User data accessible from
client only
ƒ Device-centric
ƒ Connected
ƒ Wired, sporadic
ƒ E-mail/newsgroups
ƒ Immersive, 3D interactivity
ƒ Real-time
ƒ Distributed
ƒ User data accessible
everywhere
ƒ Device-agnostic
ƒ Collaborative
ƒ Wireless, always-on
ƒ Text messaging/blogs

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Some things for Academia to look at
ƒ Specialization in computer architectures
– Beyond OS/Application, what specialization makes sense in
a general-(enough) purpose chip/system multiprocessor?
ƒ Programming paradigms and compilation techniques
to deal with memory wall
ƒ New types of applications (often real-time) made
possible by a dramatic jump in performance
– E.g. gesture and emotion recognition