[Computer Architecture] Performance

Integrated Circuit Cost

Yield : percentage of correctly working dies

Cost per die = Cost per wafer / Dies per wafer * Yield

Dies per wafer ≈ Wafer area / Die area

Yield = 1 / (1 + (Defects per area * Die area) )^N

Die area와 Cost per die는 정비례!!

Chiplet Trend

• multiple small chips
• semiconductor technology

Response Time and Throughput

Response time (latency)

• Duration

Throughput

• number of tasks

CPU Time

CPU Time = CPU Clock Cycles * Clock Cycle Time
= CPU Clock Cycles / Clock Rate

ex
2 GHz -> 2*10^9 times/sec -> 0.5ns
1 GHz -> 10^9 times/sec -> 1ns

CPU Clocking

Clock period : the duration for the clock signal toggles 1 -> 0 -> 1

Clock Frequency (rate) : The number of clock cycles per second

Instruction Count and CPI (without pipelining)

Clock Cycles = Instruction Count * Cycles Per Instruction
CPU Time = Instruction Count * CPI * Clock Cycle Time
= ( Instruction Count * CPI )/ Clock Rate

Instruction Count (IC) : Number of instructions
Cycles Per Instruction (CPI) (detemined by the processor, insturcion type)

Performance Summary

CPU Time = Seconds / Program
= Instructions / Program
= Clock cycles / Instruction
= Seconds / Clock cycle

Amdahl's Law

T(improved) = (T(affected) / improvement factor ) + T(unaffected)