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L12_advance_2010

L12_advance_2010 - Computer Architecture Advanced Topics 1...

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Computer Architecture 2010 – Advanced Topics 1 Computer Architecture Advanced Topics
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Computer Architecture 2010 – Advanced Topics 2 Pentium ® M Processor
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Computer Architecture 2010 – Advanced Topics 3 Pentium ® M Processor Intel’s 1st processor designed for mobility Achieve best performance at given power and thermal constraints Achieve longest battery life Banias Dothan transistors 77M 140M process 130nm 90nm Die size 84 mm 2 85mm 2 Peak power 24.5 watts 21 watts Freq 1.7 GHz 2.1GHz L1 cache 32KB I$ + 32KB D$ 32KB I$ + 32KB D$ L2 cache 1MB 2MB
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Computer Architecture 2010 – Advanced Topics 4 Performance per Watt Mobile’s smaller form-factor decreases power budget Power generates heat, which must be dissipated to keep transistors within allowed temperature Limits the processor’s peak power consumption Change the target Old target: get max performance New target: get max performance at a given power envelope Performance per Watt Performance via frequency increase Power = CV 2 f, but increasing f also requires increasing V X% performance costs 3X% power Assume performance linear with frequency A power efficient feature – better than 1:3 performance : power Otherwise it is better to just increase frequency All Banias u-arch features (aimed at performance) are power efficient
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Computer Architecture 2010 – Advanced Topics 5 Higher Performance vs. Longer Battery Life Processor average power is <10% of the platform The processor reduces power in periods of low processor activity The processor enters lower power states in idle periods Average power includes low-activity periods and idle-time Typical: 1W – 3W Max power limited by heat dissipation Typical: 20W – 100W Decision Optimize for performance when Active Optimize for battery life when idle Display (panel + inverter) 33% CPU 10% Power Supply 10% Intel® MCH 9% Misc. 8% GFX 8% HDD 8% CLK 5% Intel® ICH 3% DVD 2% LAN 2% Fan 2%
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Computer Architecture 2010 – Advanced Topics 6 Static Power The power consumed by a processor consists of Active power: used to switch transistors Static power: leakage of transistors under voltage Static power is a function of Number of transistors and their type Operating voltage Die temperature Leakage is growing dramatically in new process technologies Pentium ® M reduces static power consumption The L2 cache is built with low-leakage transistors (2/3 of the die transistors) Low-leakage transistors are slower, increasing cache access latency The significant power saved justifies the small performance loss Enhanced SpeedStep ® technology Reduces voltage and temperature on low processor activity
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Computer Architecture 2010 – Advanced Topics 7 Less is More Less instructions per task Advanced branch prediction reduces #wrong instructions executed SSE instructions reduce the number of instructions architecturally Less uops per instruction Uops fusion
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