02_performance

02_performance - This Unit Metrics Latency and throughput...

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CIS 501 (Martin): Performance 1 CIS 501 Computer Architecture Unit 2: Performance Slides developed by Milo Martin & Amir Roth at the University of Pennsylvania with sources that included University of Wisconsin slides by Mark Hill, Guri Sohi, Jim Smith, and David Wood. CIS 501 (Martin): Performance 2 This Unit • Metrics • Latency and throughput • Reporting performance • Benchmarking and averaging • Performance analysis & pitfalls CIS 501 (Martin): Performance 3 Readings • Chapter 1.2-1.4 of MA:FSPTCM As You Get Settled… • You drive two miles • 30 miles per hour for the first mile • 90 miles per hour for the second mile • Question: what was your average speed? • Hint: the answer is not 60 miles per hour • Why? • Would the answer be different if each segment was equal time (versus equal distance)? CIS 501 (Martin): Performance 4
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Answer • You drive two miles • 30 miles per hour for the first mile • 90 miles per hour for the second mile • Question: what was your average speed? • Hint: the answer is not 60 miles per hour • 0.03333 hours per mile for 1 mile • 0.01111 hours per mile for 1 mile • 0.02222 hours per mile on average • = 45 miles per hour CIS 501 (Martin): Performance 5 Reasoning About Performance CIS 501 (Martin): Performance 6 CIS 501 (Martin): Performance 7 Performance: Latency vs. Throughput Latency (execution time) : time to finish a fixed task Throughput (bandwidth) : number of tasks in fixed time • Different: exploit parallelism for throughput, not latency (e.g., bread) • Often contradictory (latency vs. throughput) • Will see many examples of this • Choose definition of performance that matches your goals • Scientific program? latency. web server? throughput. • Example: move people 10 miles • Car: capacity = 5, speed = 60 miles/hour • Bus: capacity = 60, speed = 20 miles/hour • Latency: car = 10 min , bus = 30 min • Throughput: car = 15 PPH (count return trip), bus = 60 PPH • Fastest way to send 10TB of data? (1+ gbits/second) CIS 501 (Martin): Performance 8 Comparing Performance • A is X times faster than B if • Latency(A) = Latency(B) / X • Throughput(A) = Throughput(B) * X • A is X% faster than B if • Latency(A) = Latency(B) / (1+X/100) • Throughput(A) = Throughput(B) * (1+X/100) • Car/bus example • Latency? Car is 3 times (and 200%) faster than bus • Throughput? Bus is 4 times (and 300%) faster than car
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Benchmarking CIS 501 (Martin): Performance 9 CIS 501 (Martin): Performance 10 Processor Performance and Workloads • Q: what does performance of a chip mean? • A: nothing, there must be some associated workload Workload : set of tasks someone (you) cares about Benchmarks : standard workloads • Used to compare performance across machines • Either are or highly representative of actual programs people run Micro-benchmarks : non-standard non-workloads • Tiny programs used to isolate certain aspects of performance • Not representative of complex behaviors of real applications
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This note was uploaded on 12/06/2011 for the course CIS 501 taught by Professor Milom during the Fall '08 term at UPenn.

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02_performance - This Unit Metrics Latency and throughput...

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