Today’s Topics
Recap
I/O performance
Laws and Principles
Performance enhancement
Concluding: quantitative principles
Home work
Summary
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Computer Architecture and Performance: I/O Systems and Amdahl's Law, Slides of Advanced Computer Architecture
An overview of computer architecture, focusing on i/o systems and performance enhancement. Topics include the producer-server model, i/o performance parameters, response time and throughput calculation, little's law, and amdahl's law. Students will gain insights into i/o system components, performance measures, and the impact of enhancements on execution time.
Typology: Slides
2011/2012
1 / 16
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Today’s Topics
Recap
I/O performance
Laws and Principles
Performance enhancement
Concluding: quantitative principles
Home work
Summary
Recap: Lecture 1-
Computer architecture verses
organization
Technological Developments
Computer design cycle
Performance metrics: time verses
throughput
Price-Performance design
Benchmarks: Performance evaluation
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
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 0. 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
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
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 Time accumulated x Number tasks = Time (^) observe Number (^) tasks Time (^) observe Mean number of tasks = mean response time x Arrival rate
Amdahl's Law
Speedup due to enhancement E:
Ex Time without E
Speedup (E) =
Ex Time with E
Performance with E
Performance without E
Amdahl’s Law
Ex Time (^) new = Ex Time (^) old x (1 – Fraction (^) enhanced) + Fraction (^) enhanced Speedup (^) enhanced
Amdahl’s Law
Floating point instructions improved to
run 2X; but only 10% of actual
instructions are FP
Speedup overall = ExTime new =
Amdahl’s Law
Floating point instructions improved to
run 2X; but only 10% of actual
instructions are FP
Speedup overall = 1
= 1. ExTime new = ExTime old x (0.9 + .1/2) = 0.95 x ExTime old
Amdahl’s Law
Speedup overall = 1
= 1. ExTime new = ExTime old x (0.9 + .1/2) = 0.95 x ExTime old