Performance Metrics - Computer Systems Performance Evaluation - Lecture Slides, Slides of Computer Science

Download Performance Metrics - Computer Systems Performance Evaluation - Lecture Slides and more Slides Computer Science in PDF only on Docsity! Performance Engineering Performance Metrics Docsity.com All About Numbers NO, I DON'T TRUST YOU WITH NUMBERS. YOU'RE THE KIND OF CAN I GET A ROUGH COST ESTIMATE FOR THE DESIGN PHASE? GUY WHO WILL REMOVE USEFUL QUALIFIERS AND DISTRIBUTE A FIGURE AS IF IT IS TRUE IN ALL CASES. DilbertCartoonist@gmail.com ©2010 Scott Adams, Inc. /Dist. by UFS, Inc. FOR EVERYONE'S SAKE, M = THE SAFEST THING T SR CAN DO IS MAKE AN MMMMM, ANNOYING HUMMING SOUND UNTILYOU GO HALF OF LIFE IS MAKING PEOPLE GO AWAY. y DECISIONS WILL BE MADE. PEOPLE WILL GET HURT. www.dilbert.com. 2210 3 Docsity.com PERFORMANCE METRICS Metric Description Formula Units Arrival Rate How many requests arrive per time. Y = A / T Requests/second Throughput (Departure Rate) How many requests complete per time. X = C / T Requests/second Utilization Fraction of time the resource is in use. U = B / T Number in range 0 - 1. Service Requirement Time needed by a resource to handle a request. S = B / C Seconds Requests in system Average number of requests in the system. N = W / T Dimensionless Residence time Average time a request spends in the system. R = W / C Seconds Docsity.com PERFORMANCE METRICS Example: Requests 3 | | 2 | ----------------- ----------------- | 1 | ----------------- ----------------- ----------------- | +---------------------------------------------------------------------------- 0 1 2 3 4 5 6 7 8 9 10 Time ( seconds ) Note that requests are serviced simultaneously - it's a multiprocessor? What are: T Time interval = A Arrivals = C Completions = B Time spent servicing = requests Y = A / T Arrival rate = X = C / T Throughput = U = B / T Utilization = S = B / C Service time/request = Docsity.com PERFORMANCE METRICS UTILIZATION LAW U = X S Proof: B / T = C / T * B / C Example: The server of dinners in the Cafeteria keeps busy 75% of the time between 12:00 and 1:00. During this time 90 people are served a dinner. How long does it take to serve each customer? Docsity.com PERFORMANCE METRICS Example: One day I was at the Weston Toll Booth on the Mass Pike. There were 10 collectors working; when I joined the line, there were 8 cars ahead of me, and when my turn came it took me 12 seconds to pay my toll. What information can be derived from the above paragraph? What information can NOT be deduced? Example: Recently in "Newsweek" it was reported that the current U.S. divorce rate is 4.6 per 1000 adults. It was also reported that half of all adults are currently married. Develop a simple model/picture in order to make some sense of these numbers. Docsity.com PERFORMANCE METRICS Some more practice problems: Example: Packets arrive at a gateway at a rate of 125 packets/second. The gateway takes an average of 2 milliseconds to forward them. What is the Throughput, Service Time, and Utilization. Example: A system has a CPU, Disk A, and Disk B. The throughputs of these devices are XCPU = 35.48, XA = 15.70, XB = 19.6. We also know that the Queue lengths are QCPU = 8.88, QA = 3.19, QB = 1.40. What are the device response times for these devices? Example: On the campus, there are a number of graduate students who have varying degree and course requirements. Build a model using duration of time until their degree, as well as the fraction of time in school. What is the service time, residence time, of a graduate student? What is the throughput of the CS Graduate School? Docsity.com PERFORMANCE METRICS SUMMARY OF PERFORMANCE METRICS T is the length of TIME we observed the system. A is the number of request ARRIVALS observed. C is the number of request DEPARTURES observed. W is the ACCUMULATED TIME for all requests within the system - time spent both waiting for and using resources. B is the length of time that the resource was observed to be BUSY. Arrival Rate Y = A / T Throughput (Departure Rate) X = C / T Utilization U = B / T Service Requirement S = B / C Requests in system N = W / T Residence time R = W / C UTILIZATION LAW U = X S LITTLE’S LAW N= X R Docsity.com