chapter5-m3-ziavras

4 cpu alpha at 128 cpus it delivers a peak bisection

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Unformatted text preview: MP = $181k + $20k * P What speedup for constant performance/cost? 8 proc = $341k; Cost(8/1)=$341k/$138k= 2.5 (cost increase) 16 proc = $501k; Cost(16/1)=$501k/$138k= 3.6 Cost(16/8)=3.6/2.5 = 1.44 44% (<100%) speedup needed ONLY needed ONLY LESS THAN LINEAR SPEEDUP NEEDED THAN LINEAR SPEEDUP NEEDED • Even if need some more memory for MP, not linear 57 • • • • • • • • Fallacy: Scalability is almost free Fallacy: Scalability is almost free • “Build scalability into a multiprocessor and then simply offer the multiprocessor at any point on the scale from a small number of processors to a large number” • Cray T3E scales to 2048 CPUs vs. 4 CPU Alpha – At 128 CPUs, it delivers a peak bisection BW of 38.4 GB/s, or At 128 CPU it bi BW 38 GB/ (38400 MB/s)/128CPUs= 300 MB/s per CPU (uses Alpha microprocessor) – Compaq Alphaserver ES40 up to 4 CPUs and has 5.6 GB/s of Al ES40 CPU GB/ interconnect BW, or 1400 MB/s per CPU • Build apps that scale requires significantly more attention – – – – load balance, locality, potential contention, contention, serial (or partly parallel) portions of program 10X is very hard 58 Pitfall: Not developing SW to take advantage (or optimize for) multiprocessor architecture (or optimize for) multip...
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