Computer Architecture

1. Computer Architecture “The architecture of a computer is the interface between the machine and the software” - Andris Padges IBM 360/370 Architect

2. Course Outline • Computer ArchitectureQuarter Autumn 2006-7 • Instructor Muhammad Jahangir Ikram • Office: Room 424 • e-mail: jikram@lums.edu.pk • Office Hours: Monday and Wednesday, 3:00 – 4:30pm

3. Course Outline (Contd..) Description This course focuses on the principles, practices and issues in Computer Architecture, while examining computer design tradeoffs both qualitatively and quantitatively. The course starts with a quick overview of computer design fundamentals and instruction set principles, the materials which the student has already covered in the pre-requisite of this course. The following topics are covered in greater detail: • Advanced Pipelining • Instruction-level parallelism and Compiler Support • Memory - hierarchy design • SIMD, VLIW, Superscalar Architectures • Code Optimization and Compiler Issues

4. Course Outline (Contd..) Text Book Hennessy, J. L, and Patterson, D. A., Computer Architecture: A Quantitative Approach, 2nd Edition. Morgan Kaufmann, 1996.

5. Course Outline (Contd..) Lectures There will be two 75 minutes lecturers per week and 50 minutes Lecture/ 100 minutes lab. TOTAL SESSIONS = 29 There will be four Labs during weeks 2, 3, 4, 5.

6. Course Outline (Contd..) Grading • Quizzes & assignments17+3% • Laboratory 10%(Atten 3 + Lab Task 3 + HW 4) • Midterm exam 30% • Final exam 40%

7. Schedule Fundamentals of Computer Design 1,2 1.1 – 1.10 • Measuring and Reporting Performance • Quantitative Principles of Computer Design Instruction Set Principles and Examples 3-5 2.1 – 2.8 • Classifying Instruction Set Architectures • Memory Addressing • Operations in the Instruction Set • Encoding an Instruction Set • LAB 1: MIPS Instruction Format and Instruction Study 6 Pipelining Overview 7-14 A.1 to A10 • What Is Pipelining? • Single Cycle Computer Study 9 • The Major Hurdle of Pipelining – Pipeline Hazards • Data Hazards • LAB 2: Study of Pipelining 12

8. Schedule • Control Hazards and Static Branch Prediction • LAB 3: Pipeline Studies and Control Hazards 15 • Scoreboarding MIDTERM ILP and Dynamic Exploitation 17-19 3.1 – 3.5 • Static Branch Prediction • Tomasulo’s Dynamic Scheduling • Dynamic Branch Prediction • Superscalar and VLIW architectures Advanced Pipelining And ILP (Cont’d.) 20-22 3.6 – 3.10 • Taking Advantage of More ILP with Multiple Issue • P6 Architecture Advanced Pipelining And ILP (Cont’d.) 23-25 4.1, 4.7 • Compiler Support for Exploiting ILP • Hardware Support for Extracting More Parallelism • Putting It All Together: The PowerPC 620, and Itanium

9. Schedule Memory-Hierarchy Design 26-29 5.1 – 5.7 • The ABCs of Caches • Reducing Cache Misses • Reducing Cache Miss Penalty • Virtual Memory System Computer I/O 30 6.1 - ?

10. Background Emergence of the first microprocessor in late 1970’s Roughly 35% growth per year Important changes in the marketplace: Virtual elimination of assembly language programming reduced the need for object code compatibility Creation of standardized, vendor-independent operating systems, such as UINX, LINX lowered the risk of bringing out a new architecture

11. Development of RISC • These changes lead to the development of a new set of architectures, called the RISC (Reduced Instruction Set Computer) architecture • RISC uses two performance techniques: • Instruction level parallelism (pipelining) • Use of Cache

12. Growth in microprocessor performance

13. Moore’s Law

14. Technology Scaling

15. Scaling of Transistors • Feature Size has reduced to 3 micron in 1985 to 0.09 micron. • Reducing Feature-size means quadratic increase in Transistor Count and better Performance. • But higher routing Delays and poor performance of Long Wires • Also means More Power Consumption (Less load Capacitance)

16. The Itanium Processor

17. Intel microprocessor die

18. IC Cost Trends (Source: IC Knowledge)

19. Measuring performance • Definition of time: • Response time, elapse time: The latency to complete the task, including disk access, input/output, operating system overhead etc. • CPU time: • User CPU Time • Time spent in the program • System CPU Time: • Time Spent by operating system. • Unix Time Command: • 90.7s 12.9s 2:39 (159s) 65% (90.7+12.9)/159 (User, System, Elapsed Time)

20. What is a Benchmark? • A benchmark is "a standard of measurement or evaluation" (Webster’s II Dictionary). • A computer benchmark is typically a computer program that performs a strictly defined set of operations - a workload - and returns some form of result - a metric - describing how the tested computer performed. • Computer benchmark metrics usually measure speed: how fast was the workload completed; or throughput: how many workload units per unit time were completed. • Running the same computer benchmark on multiple computers allows a comparison to be made. Source: Standards Performance Evaluation Corporation

21. Programs to Evaluate Performance • Real Applications • Modified (or scripted) applications • Kernels • Toy benchmarks • Synthetic benchmarks

22. Programs to evaluate performance • Real Applications • Example: Compliers for C, text-processing software etc. • Modified (or scripted) applications • CPU oriented bench mark, I/O may be removed to minimize its impact on execution

23. Programs to evaluate performance • Kernels • To isolate performance of individual features of a machine. • Toy benchmarks • Produces a result that the user already knows • Synthetic benchmarks • Try to match the average frequency of operations and operands of a large set of programs

24. Benchmark Suites • SPEC95, SPEC2000 (11 Integer, 14 FP), SPEC2006 (12 Integer, 17 FP) • C Compiler, Router, FEM • Desktop (CPU and Graphics Intensive) • Server (File Servers, Web Servers, Transaction Processing) • Embedded (EEMBC) • 34 Kernels

25. What is SPEC SPEC is the Standard Performance Evaluation Corporation. SPEC is a non-profit organization whose members include computer hardware vendors, software companies, universities, research organizations, systems integrators, publishers and consultants. SPEC's goal is to establish, maintain and endorse a standardized set of relevant benchmarks for computer systems. Although no one set of tests can fully characterize overall system performance, SPEC believes that the user community benefits from objective tests which can serve as a common reference point.

26. What does a benchmark measure? • the computer processor (CPU), • the memory architecture, and • the compilers. SPEC CPU2006 contains two components that focus on two different types of compute intensive performance: • The CINT2006 suite measures compute-intensive integer performance, and • The CFP2006 suite measures compute-intensive floating point performance Source: Standards Performance Evaluation Corporation

27. Reference Machine Source: Standards Performance Evaluation Corporation • SPEC uses a historical Sun system, the "Ultra Enterprise 2" which was introduced in 1997, as the reference machine. The reference machine uses a 296 MHz UltraSPARC II processor, as did the reference machine for CPU2000. But the reference machines for the two suites are not identical: the CPU2006 reference machine has substantially better caches, and the CPU2000 reference machine could not have held enough memory to run CPU2006. • It takes about 12 days to do a rule-conforming run of the base metrics for CINT2006 and CFP2006 on the CPU2006 reference machine. SPEC2000 now takes less a minute on latest High Performance M/Cs

28. Example Result for SPEC 2000 Source: Standards Performance Evaluation Corporation

29. Example Result for SPEC 2000Source: Standards Performance Evaluation Corporation

30. Summarizing Performance

31. Amdahl’s Law • The performance improvement to be gained from using faster mode of execution is limited by the fraction of the time the faster mode can be used

32. Amdahl’s Law: Law of Diminishing Returns

33. Instructions Clock Cycle Seconds CPU Time = Program Instruction Clock Cycle CPU performance Equations

34. Example: • Frequency of FP operations = 25% • Average CPI of FP operations = 4.0 • Average CPI of other instructions = 1.33 • Frequency of FPSQR = 2% • CPI of FPSQR = 20 • Assume CPI of FPSQR decreased to 2 OR the CPI of all FP operations to 2.5 • Compare these two designs using the CPU performance equations

35. Example: Solution CPI for enhanced FPSQR CPI for enhanced FP operation

36. Example: Solution

37. Instruction Count MIPS = 6 Execution Time  10 Another Measure -- MIPS

38. Example:An Embedded Processor • 120 MIPS for single processor. • 80 MIPS for Processor –Co-Processor Combination (That is how they are measured for combined) • I= Number of Integer Instructions • F = Number of Floating Point Instructions (8M) • Y = No. of Integer Instructions to Emulate one FP Instruction (50) • W = Time for choice 1 (4 seconds) • B = Time for Choice 2

39. End of Lecture 1

40. CINT 2006

41. CFP 2006