![Amdahl’s Law
• Gene Amdahl [AMDA67]
• Potential speed up of program using
multiple processors
• Concluded that:
—Code needs to be parallelizable
—Speed up is bound, giving diminishing returns
for more processors
• Task dependent
—Servers gain by maintaining multiple
connections on multiple processors
—Databases can be split into parallel tasks](https://image.slidesharecdn.com/02computerevolutionandperformance-221022041812-2d0924cb/85/Computer-Evolution-ppt-49-320.jpg)
Computer Evolution.ppt
- 1. William Stallings Computer Organization and Architecture 8th Edition Chapter 2 Computer Evolution and Performance
- 2. ENIAC - background • Electronic Numerical Integrator And Computer • Eckert and Mauchly • University of Pennsylvania • Trajectory tables for weapons • Started 1943 • Finished 1946 —Too late for war effort • Used until 1955
- 3. ENIAC - details • Decimal (not binary) • 20 accumulators of 10 digits • Programmed manually by switches • 18,000 vacuum tubes • 30 tons • 15,000 square feet • 140 kW power consumption • 5,000 additions per second
- 4. von Neumann/Turing • Stored Program concept • Main memory storing programs and data • ALU operating on binary data • Control unit interpreting instructions from memory and executing • Input and output equipment operated by control unit • Princeton Institute for Advanced Studies —IAS • Completed 1952
- 5. Structure of von Neumann machine
- 6. IAS - details • 1000 x 40 bit words —Binary number —2 x 20 bit instructions • Set of registers (storage in CPU) —Memory Buffer Register —Memory Address Register —Instruction Register —Instruction Buffer Register —Program Counter —Accumulator —Multiplier Quotient
- 7. Structure of IAS – detail
- 8. Commercial Computers • 1947 - Eckert-Mauchly Computer Corporation • UNIVAC I (Universal Automatic Computer) • US Bureau of Census 1950 calculations • Became part of Sperry-Rand Corporation • Late 1950s - UNIVAC II —Faster —More memory
- 9. IBM • Punched-card processing equipment • 1953 - the 701 —IBM’s first stored program computer —Scientific calculations • 1955 - the 702 —Business applications • Lead to 700/7000 series
- 10. Transistors • Replaced vacuum tubes • Smaller • Cheaper • Less heat dissipation • Solid State device • Made from Silicon (Sand) • Invented 1947 at Bell Labs • William Shockley et al.
- 11. Transistor Based Computers • Second generation machines • NCR & RCA produced small transistor machines • IBM 7000 • DEC - 1957 —Produced PDP-1
- 12. Microelectronics • Literally - “small electronics” • A computer is made up of gates, memory cells and interconnections • These can be manufactured on a semiconductor • e.g. silicon wafer
- 13. Generations of Computer • Vacuum tube - 1946-1957 • Transistor - 1958-1964 • Small scale integration - 1965 on —Up to 100 devices on a chip • Medium scale integration - to 1971 —100-3,000 devices on a chip • Large scale integration - 1971-1977 —3,000 - 100,000 devices on a chip • Very large scale integration - 1978 -1991 —100,000 - 100,000,000 devices on a chip • Ultra large scale integration – 1991 - —Over 100,000,000 devices on a chip
- 14. Moore’s Law • Increased density of components on chip • Gordon Moore – co-founder of Intel • Number of transistors on a chip will double every year • Since 1970’s development has slowed a little —Number of transistors doubles every 18 months • Cost of a chip has remained almost unchanged • Higher packing density means shorter electrical paths, giving higher performance • Smaller size gives increased flexibility • Reduced power and cooling requirements • Fewer interconnections increases reliability
- 15. Growth in CPU Transistor Count
- 16. IBM 360 series • 1964 • Replaced (& not compatible with) 7000 series • First planned “family” of computers —Similar or identical instruction sets —Similar or identical O/S —Increasing speed —Increasing number of I/O ports (i.e. more terminals) —Increased memory size —Increased cost • Multiplexed switch structure
- 17. DEC PDP-8 • 1964 • First minicomputer (after miniskirt!) • Did not need air conditioned room • Small enough to sit on a lab bench • $16,000 —$100k+ for IBM 360 • Embedded applications & OEM • BUS STRUCTURE
- 18. DEC - PDP-8 Bus Structure
- 19. Semiconductor Memory • 1970 • Fairchild • Size of a single core —i.e. 1 bit of magnetic core storage • Holds 256 bits • Non-destructive read • Much faster than core • Capacity approximately doubles each year
- 20. Intel • 1971 - 4004 —First microprocessor —All CPU components on a single chip —4 bit • Followed in 1972 by 8008 —8 bit —Both designed for specific applications • 1974 - 8080 —Intel’s first general purpose microprocessor
- 21. Speeding it up • Pipelining • On board cache • On board L1 & L2 cache • Branch prediction • Data flow analysis • Speculative execution
- 22. Performance Balance • Processor speed increased • Memory capacity increased • Memory speed lags behind processor speed
- 23. Login and Memory Performance Gap
- 24. Solutions • Increase number of bits retrieved at one time —Make DRAM “wider” rather than “deeper” • Change DRAM interface —Cache • Reduce frequency of memory access —More complex cache and cache on chip • Increase interconnection bandwidth —High speed buses —Hierarchy of buses
- 25. I/O Devices • Peripherals with intensive I/O demands • Large data throughput demands • Processors can handle this • Problem moving data • Solutions: —Caching —Buffering —Higher-speed interconnection buses —More elaborate bus structures —Multiple-processor configurations
- 26. Typical I/O Device Data Rates
- 27. Key is Balance • Processor components • Main memory • I/O devices • Interconnection structures
- 28. Improvements in Chip Organization and Architecture • Increase hardware speed of processor —Fundamentally due to shrinking logic gate size – More gates, packed more tightly, increasing clock rate – Propagation time for signals reduced • Increase size and speed of caches —Dedicating part of processor chip – Cache access times drop significantly • Change processor organization and architecture —Increase effective speed of execution —Parallelism
- 29. Problems with Clock Speed and Login Density • Power —Power density increases with density of logic and clock speed —Dissipating heat • RC delay —Speed at which electrons flow limited by resistance and capacitance of metal wires connecting them —Delay increases as RC product increases —Wire interconnects thinner, increasing resistance —Wires closer together, increasing capacitance • Memory latency —Memory speeds lag processor speeds • Solution: —More emphasis on organizational and architectural approaches
- 31. Increased Cache Capacity • Typically two or three levels of cache between processor and main memory • Chip density increased —More cache memory on chip – Faster cache access • Pentium chip devoted about 10% of chip area to cache • Pentium 4 devotes about 50%
- 32. More Complex Execution Logic • Enable parallel execution of instructions • Pipeline works like assembly line —Different stages of execution of different instructions at same time along pipeline • Superscalar allows multiple pipelines within single processor —Instructions that do not depend on one another can be executed in parallel
- 33. Diminishing Returns • Internal organization of processors complex —Can get a great deal of parallelism —Further significant increases likely to be relatively modest • Benefits from cache are reaching limit • Increasing clock rate runs into power dissipation problem —Some fundamental physical limits are being reached
- 34. New Approach – Multiple Cores • Multiple processors on single chip —Large shared cache • Within a processor, increase in performance proportional to square root of increase in complexity • If software can use multiple processors, doubling number of processors almost doubles performance • So, use two simpler processors on the chip rather than one more complex processor • With two processors, larger caches are justified —Power consumption of memory logic less than processing logic
- 35. x86 Evolution (1) • 8080 — first general purpose microprocessor — 8 bit data path — Used in first personal computer – Altair • 8086 – 5MHz – 29,000 transistors — much more powerful — 16 bit — instruction cache, prefetch few instructions — 8088 (8 bit external bus) used in first IBM PC • 80286 — 16 Mbyte memory addressable — up from 1Mb • 80386 — 32 bit — Support for multitasking • 80486 — sophisticated powerful cache and instruction pipelining — built in maths co-processor
- 36. x86 Evolution (2) • Pentium — Superscalar — Multiple instructions executed in parallel • Pentium Pro — Increased superscalar organization — Aggressive register renaming — branch prediction — data flow analysis — speculative execution • Pentium II — MMX technology — graphics, video & audio processing • Pentium III — Additional floating point instructions for 3D graphics
- 37. x86 Evolution (3) • Pentium 4 — Note Arabic rather than Roman numerals — Further floating point and multimedia enhancements • Core — First x86 with dual core • Core 2 — 64 bit architecture • Core 2 Quad – 3GHz – 820 million transistors — Four processors on chip • x86 architecture dominant outside embedded systems • Organization and technology changed dramatically • Instruction set architecture evolved with backwards compatibility • ~1 instruction per month added • 500 instructions available • See Intel web pages for detailed information on processors
- 38. Embedded Systems ARM • ARM evolved from RISC design • Used mainly in embedded systems —Used within product —Not general purpose computer —Dedicated function —E.g. Anti-lock brakes in car
- 39. Embedded Systems Requirements • Different sizes —Different constraints, optimization, reuse • Different requirements —Safety, reliability, real-time, flexibility, legislation —Lifespan —Environmental conditions —Static v dynamic loads —Slow to fast speeds —Computation v I/O intensive —Descrete event v continuous dynamics
- 40. Possible Organization of an Embedded System
- 41. ARM Evolution • Designed by ARM Inc., Cambridge, England • Licensed to manufacturers • High speed, small die, low power consumption • PDAs, hand held games, phones —E.g. iPod, iPhone • Acorn produced ARM1 & ARM2 in 1985 and ARM3 in 1989 • Acorn, VLSI and Apple Computer founded ARM Ltd.
- 42. ARM Systems Categories • Embedded real time • Application platform —Linux, Palm OS, Symbian OS, Windows mobile • Secure applications
- 43. Performance Assessment Clock Speed • Key parameters —Performance, cost, size, security, reliability, power consumption • System clock speed —In Hz or multiples of —Clock rate, clock cycle, clock tick, cycle time • Signals in CPU take time to settle down to 1 or 0 • Signals may change at different speeds • Operations need to be synchronised • Instruction execution in discrete steps —Fetch, decode, load and store, arithmetic or logical —Usually require multiple clock cycles per instruction • Pipelining gives simultaneous execution of instructions • So, clock speed is not the whole story
- 44. System Clock
- 45. Instruction Execution Rate • Millions of instructions per second (MIPS) • Millions of floating point instructions per second (MFLOPS) • Heavily dependent on instruction set, compiler design, processor implementation, cache & memory hierarchy
- 46. Benchmarks • Programs designed to test performance • Written in high level language —Portable • Represents style of task —Systems, numerical, commercial • Easily measured • Widely distributed • E.g. System Performance Evaluation Corporation (SPEC) —CPU2006 for computation bound – 17 floating point programs in C, C++, Fortran – 12 integer programs in C, C++ – 3 million lines of code —Speed and rate metrics – Single task and throughput
- 47. SPEC Speed Metric • Single task • Base runtime defined for each benchmark using reference machine • Results are reported as ratio of reference time to system run time —Trefi execution time for benchmark i on reference machine —Tsuti execution time of benchmark i on test system • Overall performance calculated by averaging ratios for all 12 integer benchmarks —Use geometric mean – Appropriate for normalized numbers such as ratios
- 48. SPEC Rate Metric • Measures throughput or rate of a machine carrying out a number of tasks • Multiple copies of benchmarks run simultaneously — Typically, same as number of processors • Ratio is calculated as follows: — Trefi reference execution time for benchmark i — N number of copies run simultaneously — Tsuti elapsed time from start of execution of program on all N processors until completion of all copies of program — Again, a geometric mean is calculated
- 49. Amdahl’s Law • Gene Amdahl [AMDA67] • Potential speed up of program using multiple processors • Concluded that: —Code needs to be parallelizable —Speed up is bound, giving diminishing returns for more processors • Task dependent —Servers gain by maintaining multiple connections on multiple processors —Databases can be split into parallel tasks
- 50. Amdahl’s Law Formula • Conclusions —f small, parallel processors has little effect —N ->∞, speedup bound by 1/(1 – f) – Diminishing returns for using more processors • For program running on single processor —Fraction f of code infinitely parallelizable with no scheduling overhead —Fraction (1-f) of code inherently serial —T is total execution time for program on single processor —N is number of processors that fully exploit parralle portions of code
- 51. Internet Resources • http://www.intel.com/ —Search for the Intel Museum • http://www.ibm.com • http://www.dec.com • Charles Babbage Institute • PowerPC • Intel Developer Home
- 52. References • AMDA67 Amdahl, G. “Validity of the Single-Processor Approach to Achieving Large-Scale Computing Capability”, Proceedings of the AFIPS Conference, 1967.