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CPU OVERHEAD III
Data
(fixed work)
Last Modified:  24 May 2001

Below is the test data taken relative to CPU overhead using a  fixed work  method.
Test Paramters:
    two nested for loops - partial outer cycle and 717,221,000
    nine total timing runs with first thrown away (resulting run times approximate CPU overhead II testing for 150,300 ns between interrupts)

Results:
    average cost to user per interrupt:  11,120 nanoseconds
    sample standard deviation:                   333 nanoseconds
 
 
 

 
TIME BETWEEN
INTERRUPTS* ns
TARGET NUMBER
AVERAGE WALL CLOCK 
PERCENT
COST PER
DATA SET
[RTC units]
OF INTERRUPTS
TIME USED(micros)&&
USER TIME
INTERRUPT+ (ns)
0
--
0
6,460,390
100.00
--
1
300,600 [600]
599,000
6,709,270
96.36
10,942
2
275,550 [550]
654,000
6,726,860
96.11
10,719
3
250,500 [500]
719,000
6,759,590
95.64
10,922
4
225,450 [450]
799,000
6,792,480
95.18
10,867
5
200,400 [400]
899,000
6,862,860
94.21
11,603
6
175,350 [350]
1,027,000
6,890,950
93.82
10,837
7
150,300 [300]
1,198,000
6,976,280
92.67
11,017
8
125,250 [250]
1,438,000
7,080,380
91.31
10,884
9
100,200 [200]
1,797,000
7,367,520
87.75
12,274
10
75,150 [150]
2,396,000
7,580,220
85.29 
11,054
11
50100 [100]
3,593,000
8,312,040
77.78
11,132
12
45,090 [90]
3,993,000
8,574,300
75.40
11,092
13
40,080 [80]
4,492,000
8,905,400
72.60
10,982
14
35,070 [70]
5,133,000
9,415,130
68.67
10,987
15
32,565 [65]
5,528,000
9,789,040
66.04
11,059
16
30,060 [60]
5,989,000
10,487,300 
 61.65
11,528
17
27,555 [55]
6,533,000
10,837,600
 59.66
11,116
18
25,050 [50]
7,186,000
 11,642,000
 55.53
11,140
19
22,545 [45]
7,985,000
 12,733,000
50.78
11,097
20
 22,040 [40]
8,157,000
 14,489,600
 44.62
11,098
21
17,535 [35]
10,266,000
 17,820,900
 36.28
11,173

*       "TIME BETWEEN" is based on 501 nanoseconds per Myrinet card RTC unit.  So it is (RTC units) * 501.   Number in "[ ]" is the RTC units.
&&  Nine runs of seven seconds each.  First run is not counted in average.
+        Based on (RTC units * 501)*(1-(percent user time)/100)
 
 



Bill Lawry