PlayStation2 as a General Purpose Computer

1
PlayStation2 as a General Purpose Computer

• (The Emotion Engine vs. general PC architectures)

2
Can the PlayStation2 compete with the PC as a
general purpose computer?

• Whats the difference between the general PC
  architecture and the PlayStation2 architecture?
• How do these differences affect the performance
  of the PlayStation2 on general applications like
  word processing and running email clients?

3
SISD vs. SIMD

• SISD Single Instruction stream Single Data
  stream
• Intel and AMD Processors
• SIMD Single Instruction stream Multiple Data
  streams
• PlayStation2
• Motorola's MPC7400 (the G4)
• Sun's MAJC

4
SISD

• Takes advantage of instruction-level parallelism
• Executes multiple instructions at once on the
  same data stream
• Good performance depends on good cache
  performance
• Very high clock speed (execute as many
  instructions as you can as fast as possible)

5
SIMD

• Takes advantage of data parallelism
• Executes the same instruction on large amounts of
  uniform data all at once
• Good performance depends on efficiently packing
  data into uniform format
• Slower clock speed
• Very high throughput

6
SISD/SIMD
7
SIMD on the PlayStation2

• The heart of the PlayStation2 is the Emotion
  Engine
• Its main function is to calculate display lists
  and send them on to a Graphics Synthesizer which
  renders these lists into three dimensional
  objects

8
SIMD on the PlayStation2

• Calculating display lists basically involves
  vector calculations
• the kind of task a SIMD architecture is perfect
  for
• It requires a relatively small set of
  instructions operating on massive amounts of
  uniform data
• The most common operation is a tight loop
  iterating through sets of matrices

9
Differences in cache implementation

• SISD data caches tend to be large
• Huge performance gains are achieved by reading in
  a big chunk of data and executing as many
  instructions as you can on it
• This approach is terrible for SIMD architecture
• Data is not referenced repeatedly
• Vector calculations are performed and then the
  next bit of data is read
• Nothing is gained by storing old data in cache
  memory

10
Cache specs for the Pentium 4 (SISD
architecture)

• 12K µop 8-way set associative execution trace
  cache
• 8K 8-way set associative data cache
• 256K or 512K 8-way set associative Level 2 cache
• The exact size of the L1 instruction cache is not
  clearly documented (8-12K would be a reasonable
  assumption)

11
Cache specs for Emotion Engine(SIMD architecture)

• 16K 2-way set associative instruction cache
• 8K 2-way set associative data cache
• Two Vector Units (VU0 and VU1) each have a 16K
  instruction cache and 16K data cache
• 16K SPRAM (Scratch Pad RAM - high speed memory
  shared by the processor and VU0

12
Cache Specs

• The PlayStation total cache size is smaller than
  the Pentium 4 by a factor of about 3 or 5
  depending on the size of the Pentium L2 cache
• Also, the caches are divided up into much smaller
  units on the Emotion Engine
• The big difference is the lack of a L2 cache in
  the Emotion Engine

13
Bandwith in the Emotion Engine

• Designed with massive bandwith to maximize
  throughput
• Memory bus bandwith 3.2 GB/s
• 16-bit bus connects two 128 MB RDRAM memory banks
  to the 10-channel Direct Memory Access Controller
  (DMAC)
• DMAC allows up to 10 simultaneous data transfers
  on 128-bit and 64-bit buses
• Much higher throughput is achieved because the
  system can service more requests simultaneously

14
General Purpose SISD Architecture
15
Emotion Engine Architecture
16
Performance of the PlayStation2

• In multi media applications
• Outperforms PCs by far on tasks such as
• mp3 encoding/decoding
• mpeg encoding/decoding
• graphics applications
• In applications that have very little data
  parallelism (like word processing, email, or
  internet browsing)
• Degenerates to a machine with very low clock rate
  and a terrible cache implementation
• Cannot possibly compete with modern PCs

17
Can the PlayStation2 compete with general purpose
CPUs?

• Not currently
• The lack of a L2 cache makes it difficult to
  compete with SISD architectures on workloads with
  high data reuse
• Even if we focus entirely on multimedia
  applications
• Code would have to be re-written and re-compiled
  to take advantage of the Emotion Engines higher
  bandwith and vector processors
• Not enough memory
• Only supports a total of 32MB
• Not enough permanent storage
• Max storage capacity is 16MB (two 8MB memory
  cards)

18
Some Necessary Improvements

• Several improvements are necessary if the
  PlayStation2 wants to compete with general
  purpose PCs in the future. For example
• Memory hierarchy needs to be re-designed to
  accommodate SISD workloads
• A level 2 cache and a trace execution cache would
  substantially improve performance
• A more powerful core CPU is necessary
• Wider issue
• Improved branch predictor
• Programmers need to learn how to fully utilize
  the strengths of the Emotion Engine Architecture

19
In the Future

• The PlayStation2 will face tougher competition
  from PC architectures, like the G4, that are
  incorporating SIMD architectures into their
  design more aggressively
• It will be interesting to see how these new
  architectures compete with the PlayStation2 as 3D
  gaming systems

20
References

• Jon Hannibal Stokes
• Sound and Vision A Technical Overview of the
  Emotion Engine
• http//www.arstechnica.com/reviews/1q00/playstatio
  n2/ee-1.html
• The PlayStation2 vs. the PC a System-level
  Comparison of Two 3D Platforms
• http//www.arstechnica.com/cpu/2q00/ps2/ps2vspc-1.
  html
• 3 1/2 SIMD Architectures
• http//www.arstechnica.com/cpu/1q00/simd/simd-1.ht
  ml
•  A microprocessor with a 128-bit CPU, ten
  floating-point MAC's, four floating-point
  dividers, and an MPEG-2 decoder Suzuoki, M.
  Kutaragi, K. et alSolid-State Circuits, IEEE
  Journal of , Volume 34 Issue 11 , Nov. 1999
  Page(s) 1608 -1618
• Vector unit architecture for emotion synthesis
  Kunimatsu, A. Ide, N. Sato, T. Endo, Y.
  Murakami, H. Kamei, T. Hirano, M. Ishihara,
  F. Tago, H. Oka, M. Ohba, A. Yutaka, T.
  Okada, T. Suzuoki, M. IEEE Micro , Volume 20
  Issue 2 , March-April 2000 Page(s) 40 -47
• Designing and programming the emotion engine
  Oka, M. Suzuoki, M. IEEE Micro , Volume 19
  Issue 6 , Nov.-Dec. 1999 Page(s) 20 -28