1 / 22

Computer Architecture & Operations I

Instructor: Yaohang Li. Computer Architecture & Operations I. Review. Last Class Program and Computer Compiler, Assembler, and Linker Components of a Computer This Class Quiz 1 Definition of Computer Performance Measure of Computer Performance Next Class Power Wall Assignment 1.

shiro
Download Presentation

Computer Architecture & Operations I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Instructor: Yaohang Li Computer Architecture & Operations I

  2. Review • Last Class • Program and Computer • Compiler, Assembler, and Linker • Components of a Computer • This Class • Quiz 1 • Definition of Computer Performance • Measure of Computer Performance • Next Class • Power Wall • Assignment 1

  3. An Analogy §1.4 Performance • Which airplane has the best performance?

  4. Answer • That depends on … • If performance means • “the least time of transferring 1 passenger from one place to another” • Concorde • “the least time of transferring 450 passenger from one place to another” • Boeing 747 • Performance can be defined in different ways

  5. Response Time and Throughput • Response time (AKA Execution Time) • Total time required for a computer to complete a task • Measured by time • Throughput (AKA Bandwidth) • Number of tasks done work done per unit time • e.g., tasks/transactions/… per hour

  6. Response Time and Throughput • Assuming each task in a computer is a serial task. How are response time and throughput affected by • Replacing with a faster processor? • Reduce response time • Increase throughput • Adding more processors? • Increase throughput • Same response time • We’ll focus on response time for now…

  7. Performance and Execution Time • Performance

  8. Relative Performance • “X is n time faster than Y” • Example: time taken to run a program • 10s on A, 15s on B • Execution TimeB / Execution TimeA= 15s / 10s = 1.5 • So A is 1.5 times faster than B

  9. Measuring Execution Time • Elapsed (Wallclock) time • Total response time, including all aspects • Processing, I/O, OS overhead, idle time • Determines system performance • CPU time • Time spent processing a given job • Discounts I/O time, other jobs’ shares • Comprises user CPU time and system CPU time • User CPU time: CPU time spent in a program itself • System CPU time: CPU time spent in the OS performing task on behalf of the program • Different programs are affected differently by CPU and system performance

  10. CPU Clocking • Operation of digital hardware governed by a constant-rate clock Clock period Clock (cycles) Data transferand computation Update state • Clock period: duration of a clock cycle • e.g., 250ps = 0.25ns = 250×10–12s • Clock frequency (rate): cycles per second • e.g., 4.0GHz = 4000MHz = 4.0×109Hz

  11. CPU Time

  12. Performance Improvement • Performance improved by either • Increasing clock rate • => Shorter clock period • => More but shorter instructions • => More clock cycles • Reducing number of clock cycles • => Longer clock period • => Less but Longer Instructions • => Reducing clock rate • Hardware designer must often trade off clock rate against cycle count

  13. CPU Time Example • A Program on Computer A: 2GHz clock, 10s CPU time • Designing Computer B • Aim for 6s CPU time • Can do faster clock, but causes 1.2 × clock cycles • How fast must Computer B clock be?

  14. Instruction Set Architecture • Instruction Set Architecture (ISA) • An abstract interface between the hardware and the lowest-level software that encompasses all the information necessary to write a machine language program that will run correctly • Repertoire of instructions • Registers • Memory access • I/O

  15. Clock Cycles per Instruction (CPI) • Clock Cycles per Instruction (CPI) • Average number of clock cycles per instruction for a program

  16. Instruction Count and CPI • Instruction Count (IC) for a program • Determined by program, ISA and compiler • Average cycles per instruction • Determined by CPU hardware • If different instructions have different CPI • Average CPI affected by instruction mix

  17. CPI Example • Computer A: Cycle Time = 250ps, CPI = 2.0 • Computer B: Cycle Time = 500ps, CPI = 1.2 • Same ISA • Which is faster, and by how much? A is faster… …by this much

  18. CPI in More Detail • If different instruction classes take different numbers of cycles • Weighted average CPI Relative frequency

  19. CPI Example • Alternative compiled code sequences using instructions in classes A, B, C • Sequence 1: IC = 5 • Clock Cycles= 2×1 + 1×2 + 2×3= 10 • Avg. CPI = 10/5 = 2.0 • Sequence 2: IC = 6 • Clock Cycles= 4×1 + 1×2 + 1×3= 9 • Avg. CPI = 9/6 = 1.5

  20. Summary • Response Time and Throughput • Performance Measure • CPI (Cycles per Instruction) • IC (Instructions Count) • Performance Definition

  21. What I want you to do • Review Chapter 1

More Related