SLIDE 1
1 Processor Performance and Parallelism Processor Performance and Parallelism
Slides by YashwantMalaiya Limited content from:
Computer Architecture
A Quantitative Approach Hennessy, Patterson
Processor Execution time Processor Execution time
The time taken by a program to execute is the product of
n Number of machine instructions executed n Number of clock cycles per instruction (CPI) n Single clock period duration
Example: 10,000 instructions, CPI=2, clock period = 250 ps The time taken by a program to execute is the product of
n Number of machine instructions executed n Number of clock cycles per instruction (CPI) n Single clock period duration
Example: 10,000 instructions, CPI=2, clock period = 250 ps
period Clock CPI Count n Instructio Time CPU n Instructio per Cycles Count n Instructio Cycles Clock × × = × = . sec 6 10 . 5 12 10 . 250 2 4 10 250 000 , − = − × × = × × = ps ns instructio 2 1 Time CPU
CS 270 - Spring Semester 2016
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Processor Execution time Processor Execution time
Instruction Count for a program
n Determined by program, ISA and compiler
Average Cycles per instruction (CPI)
n Determined by C
PU hardw are
n If different instructions have different CPI
Average CPI affected by instruction m ix
Clock cycle time (inverse of frequency)
n Logic levels n technology
Instruction Count for a program
n Determined by program, ISA and compiler
Average Cycles per instruction (CPI)
n Determined by C
PU hardw are
n If different instructions have different CPI
Average CPI affected by instruction m ix
Clock cycle time (inverse of frequency)
n Logic levels n technology
Time Cycle Clock CPI Count n Instructio Time CPU × × =
CS 270 - Spring Semester 2016
3
Reducing clock cycle time Reducing clock cycle time
Has worked well for decades. Small transistor dimensions implied smaller delays and hence lower clock cycle time. Not any more. Has worked well for decades. Small transistor dimensions implied smaller delays and hence lower clock cycle time. Not any more.
CS 270 - Spring Semester 2016
4