Time Scales P382 Absolute Time Typically use nanoseconds 10-9 seconds Time scale of computer instructions
6 Time Scales P382 • Absolute Time – Typically use nanoseconds • 10–9 seconds – Time scale of computer instructions
Time Scales Clock Cycles Most computers controlled by high frequency clock signal Typical Range 100 MHZ 108 cycles per second Clock period = 10ns ·26Hz 2 X 109 cycles per second Clock period =0.5ns
7 Time Scales • Clock Cycles – Most computers controlled by high frequency clock signal – Typical Range • 100 MHz – 108 cycles per second – Clock period = 10ns • 2 GHz – 2 X 109 cycles per second – Clock period = 0.5ns
CPE P383 1 void vsuml (int n) 2{ in七i 345678 for(i=0;主<n;i++) c[i]=a[i]+b[i];
8 CPE P383 1 void vsum1(int n) 2 { 3 int i; 4 5 for (i = 0; i < n; i++) 6 c[i] = a[i] + b[i]; 7 } 8
CPE P383 9/* Sum vector of n elements (n must be even)*/ 10 void vsum2 (int n) 11{ 12 int i 13 14 for(主=0;i<n;i+=2){ 15 /* Compute two elements per iteration * 16 cli= ali] bli] 17 c[i+1]=a[i+1]+b[i+1]; 18 19}
9 CPE P383 9 /* Sum vector of n elements (n must be even) */ 10 void vsum2(int n) 11 { 12 int i; 13 14 for (i = 0; i < n; i+=2) { 15 /* Compute two elements per iteration */ 16 c[i] = a[i] + b[i]; 17 c[i+1] = a[i+1] + b[i+1]; 18 } 19 }
Cycles per element Convenient way to express performance of program that operators on vectors or lists Length = n T= CPE 大n+ Overhea
10 Cycles Per Element • Convenient way to express performance of program that operators on vectors or lists • Length = n • T = CPE*n + Overhead