高级计算机体系结构设计及其在数据中心和云计算的应用PerformanceLatency (execution time):time to finish one taskThroughput (bandwidth): number of tasks/unit time- Throughput can exploit parallelism, latency can't-Sometimescomplimentary,often contradictoryExample: move people from A to B, 10 miles- Car: capacity=5, speed =60 miles/hour- Bus:capacity= 60, speed = 20 miles/hour-Latency:car=10min,bus=30min Throughput: car = 15 PPH (count return trip), bus = 60 PPHNo right answer:pick metricforyour goals
高级计算机体系结构设计及其在数据中心和云计算的应 用 Performance • Latency (execution time): time to finish one task • Throughput (bandwidth): number of tasks/unit time – Throughput can exploit parallelism, latency can’t – Sometimes complimentary, often contradictory • Example: move people from A to B, 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 No right answer: pick metric for your goals
高级计算机体系结构设计及其在数据中心和云计算的应用Performance Improvement. Processor Ais Xtimes faster than processor B if- Latency(P,A) = Latency(P,B) / X Throughput(P,A) = Throughput(P,B) * XProcessorAisX%fasterthanprocessorBif Latency(P,A) = Latency(P,B) / (1+X/100) Throughput(P,A) = Throughput(P,B) * (1+X/100)·Car/bus example Latency? Car is 3 times (200%) faster than bus Throughput? Bus is 4 times (300%) faster than car
高级计算机体系结构设计及其在数据中心和云计算的应 用 Performance Improvement • Processor A is X times faster than processor B if – Latency(P,A) = Latency(P,B) / X – Throughput(P,A) = Throughput(P,B) * X • Processor A is X% faster than processor B if – Latency(P,A) = Latency(P,B) / (1+X/100) – Throughput(P,A) = Throughput(P,B) * (1+X/100) • Car/bus example – Latency? Car is 3 times (200%) faster than bus – Throughput? Bus is 4 times (300%) faster than car