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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
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 Examples: binary tree search, towers-of-hanoi, 8-queens, etc.

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

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