1. Lecture 1: Introduction CprE 585 Advanced Computer Architecture, Fall 2004 Zhao Zhang

2. Traditional “Computer Architecture” The term architecture is used here to describe the attribute of a system as seen by the programmer, i.e., the conceptual structure and functional behavior as distinct from the organization of the data flow and controls, the logic design, and the physical implementation. Gene Amdahl, IBM Journal R&D, April 1964

3. Contemporary “Computer Architecture” Instruction set architecture: program-visible instruction set Instruction format, memory addressing modes, architectural registers, endian type, alignment, … EX: RISC, CISC, VLIW, EPIC Organization: high-level aspects of a computer’s design Pipeline structure, instruction scheduling, cache, memory, disks, buses, etc. Implementations: the specifics of a machine Logic design, packaging technology

4. Fundamentals ISA design principles and performance evaluation The impacts of technology trends and market factors Performance evaluation methodologies

5. High Performance Computer Architecture Given a huge number of transistors, how to run programs as rapid as possible? Sequential Programs Parallel and multiprogramming programs

6. Instruction Level Parallelism Sequential program performance: Execution Time = #inst × CPI × Cycle time Pipelining works well for sequential programs But best Performance limited by CPI >= 1.0 Pipeline hazards draws back performance

7. Multi-issue Pipeline Naïve extension to multi-issue IF ID EX MEM WB IF ID EX MEM WB IF ID EX MEM WB IF ID EX MEM WB IF ID EX MEM WB

8. Pipeline Efficiency for (i=0; i<N; i++) X[i] = a*X[i]; // let R3=&X[0],R4=&X[N] // and F0=a LOOP: LD.D F2, 0(R3) MUL.D F2, F2, F0 S.D F2, 0(R3) DADD R3, R3, 8 BNE R3, R4, LOOP How much parallelism exist in the program? What’s the problem with the naïve multi- issue pipeline? Data hazards Control hazards

9. How to Exploit ILP? Find independent instructions through dependence analysis Hardware approaches => Dynamically scheduled superscalar Most commonly used today: Intel Pentium, AMD, Sun UltraSparc, and MIPS families Software approaches => (1) Static scheduled superscalar, or (2) VLIW

10. Dynamically Scheduled Superscalar Important features: Multi-issue and Deep pipelining Dynamic scheduling Speculative execution Branch prediction Memory dependence speculation Non-blocking caches High bandwidth caches

11. Dynamically Scheduled Superscalar Challenges: Complexity!!! Key issues: Understand why it is correct Know dependences Will prove that dynamic execution is “correct” Understand how it brings high performance Will see wield designs Will use Verilog, simulation to help understanding Have big pictures

12. A typical memory hierarchy today: Here we focus on L1/L2/L3 caches, virtual memory and main memory Memory System Performance Proc/Regs L1-Cache L2-Cache Memory Disk, Tape, etc. BiggerFaster L3-Cache (optional)

13. Memory System Performance Memory Stall CPI = Miss per inst × miss penalty = % Mem Inst × Miss rate × Miss Penalty Assume 20% memory instruction, 2% miss rate, 400-cycle miss penalty. How much is memory stall CPI?

14. Cache Design Many applications are memory-bound CPU speeds increases fast; memory speed cannot match up Cache hierarchy: exploits program locality Basic principles of cache designs Hardware cache optimizations Application cache optimizations Prefetching techniques Also talk about virtual memory

15. High Performance Storage Systems What limits the performance of web servers? Storage! Storage technology trends RAID: Redundant array of inexpensive disks

16. Multiprocessor Systems Must exploit thread-level parallelism for further performance improvement Shared-memory multiprocessors: Cooperating programs see the same memory address How to build them? Cache coherence Memory consistency

17. Other Topics VLIW basics and modern VLIW processors Simultaneous multithreading and chip-level multiprocessing Low power processor design Circuit issues in high-performance processor Other selected topics

18. Why Study Computer Architecture As a hardware designer/researcher – know how to design processor, cache, storage, graphics, interconnect, and so on As a system designer – know how to build a computer system using the best components available As a software designer – know how to get the best performance from the hardware