Advanced Computer Architecture - Lecture 3: Quantitative principles (Cont’d). This lecture will cover the following: design for performance; I/O performance; laws and principles; performance enhancement; concluding: quantitative principles;...
CS 704 Advanced Computer Architecture Lecture 3 Quantitative Principles … Cont’d Design for Performance Prof Dr M Ashraf Chughtai MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd Today’s Topics Recap I/O performance Laws and Principles Performance enhancement Concluding: quantitative principles Home work Summary MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd Recap: Lecture 1-2 Computer architecture verses organization Technological Developments Computer design cycle Performance metrics: time verses throughput Price-Performance design Benchmarks: Performance evaluation MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd Computer I/O System Producer-Server model – Producer: the device that generates request to be serviced – Queue: the area where the tasks accumulate waiting to be serviced – Server: the device performing the requested service – Response Time: the time a task takes from the moment it is placed in the buffer to the time server finishes the task Producer Arrivals MAC/VU-Advanced Computer Architecture Queue Server departures Lecture - Performance Cont'd I/O device/ controller I/O Performance Parameters Diversity: Which I/O device can connect to the CPU Capacity: How many I/O devices can connect to the CPU Latency: Overall response time to complete a task Bandwidth: Number of task completed in specified time - throughput MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd I/O Transaction Time The interaction time or transaction time of a computer is sum of three times: – Entry Time: the time for user to enter a command – average 25 sec; from keyboard 4.0 sec – System Response Time: time between when user enters the command and system responds – Think Time: the time from reception of the command until the user enters the next command MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd Response time – latency ms Throughput verses Response time: 200 _ 150 _ 100 _ 50 _ 20 Performance Measures Cont’d | 0% | 20% | 40% | 60% | 80% | 100% % of maximum throughput - bandwidth MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd Response time and throughput calculation Arrivals Departures If the system is in steady state, then the number of tasks entering the system must be equal to the number of tasks leaving the system Little’s Law: Mean number of tasks in system = Mean response time x Arrival rate MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd Little’s Law – A Little queuing theory Mean number of tasks in the system = (Time accumulated) / (Time observe) Mean response time = (Time accumulated) / (Number tasks) Arrival rate λ = (Number tasks) / (Time observe) The expression for mean number of task may be written as: Time accumulated Timeaccumulated x Number tasks = Time observe Number tasks Time observe Mean number of tasks response time x Arrival rate Lecture= - mean Performance Cont'd MAC/VU-Advanced Computer Architecture Amdahl's Law Suppose that enhancement E accelerates a fraction F of the task by a factor S, and the remainder of the task is unaffected Time for Fraction F to be Enhanced by factor S Original Execution Time of Task MAC/VU-Advanced Computer Architecture Execution time of the Fraction Enhanced Execution Time after fraction F Enhanced by factor S Lecture - Performance Cont'd 10 Amdahl's Law Speedup due to enhancement E: Ex Time without E Speedup (E) = Ex Time with E Performance with E = MAC/VU-Advanced Computer Architecture Performance without E Lecture - Performance Cont'd 11 Amdahl’s Law Ex Time new = Ex Time old x (1 – Fraction enhanced) + Fraction enhanced Speedup enhanced MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd 12 Amdahl’s Law ExTimenew = ExTimeold x (1 - Fractionenhanced) + Fractionenhanced Speedupenhanced Speedupoverall = MAC/VU-Advanced Computer Architecture ExTimeold ExTimenew = (1 - Fractionenhanced) + Fractionenhanced Lecture - Performance Cont'd Speedupenhanced 13 Amdahl’s Law Floating point instructions improved to run 2X; but only 10% of actual instructions are FP ExTimenew = Speedupoverall = MAC/VU-Advanced Computer Architecture Lecture - Performance Cont'd 14 Amdahl’s Law Floating point instructions improved to run 2X; but only 10% of actual instructions are FP ExTimenew = ExTimeold x (0.9 + 1/2) = 0.95 x ExTimeold Speedupoverall = MAC/VU-Advanced Computer Architecture 0.95 Lecture - Performance Cont'd = 1.053 15 Amdahl’s Law ExTimenew = ExTimeold x (1 - Fractionenhanced) + Fractionenhanced Speedupenhanced Speedupoverall = MAC/VU-Advanced Computer Architecture ExTimeold ExTimenew = (1 - Fractionenhanced) + Fractionenhanced Lecture - Performance Cont'd Speedupenhanced 16 Amdahl’s Law Solution ExTimenew = ExTimeold x (0.9 + 1/2) = 0.95 x ExTimeold Speedupoverall = MAC/VU-Advanced Computer Architecture 0.95 Lecture - Performance Cont'd = 1.053 17 ... and Principles Performance enhancement Concluding: quantitative principles Home work Summary MAC/VU -Advanced Computer Architecture Lecture - Performance Cont'd Recap: Lecture 1-2 Computer architecture. .. MAC/VU -Advanced Computer Architecture Lecture - Performance Cont'd 12 Amdahl’s Law ExTimenew = ExTimeold x (1 - Fractionenhanced) + Fractionenhanced Speedupenhanced Speedupoverall = MAC/VU -Advanced. .. completed in specified time - throughput MAC/VU -Advanced Computer Architecture Lecture - Performance Cont'd I/O Transaction Time The interaction time or transaction time of a computer is sum of three