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I am trying to use GNU coreutil top's formula for calculating CPU usages in percentage. But top is using some half_total, to calculate the percentage, which is adding 0.5 to the percentage.
In utils.c of top's source, the following line (at 3.8 beta1, it is in line number: 459): -
*out++ = (int)((*diffs++ * 1000 + half_total) / total_change);
This translates to : ( (*diffs++ * 1000) / total_change ) + 1/2 So, it always gives a number, which is: "10 times the percentage, plus 0.5". So if the percentage is x, it will return 10x+0.5.
Can anyone explain how is this average calculated? or at least some pointer where I can get the help?
PS:
Why can't we just use (*diffs++/total_change) * 100 to get the required percentage?
Top's source code is located at: - http://downloads.sourceforge.net/unixtop/top-3.8beta1.tar.gz?modtime=1210117842&big_mirror=0
457
The calculated CPU time that is derived from the reported consumed CPU time divided by the reported available capacity is 50% (45 seconds divided by 90 seconds). The interactive utilization percentage is 17% (15 seconds divided by 90 seconds). The batch utilization percentage is 33% (30 seconds divided by 90 seconds).
This is the way to do rounding for integer values, because the division discards the fractional part.
When you add half the divisor this is equivalent to a floating point division and rounding up if the fractional part is 0.5 or greater.
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