top命令的CPU使用率计算 [英] top command's CPU usage calculation

问题描述

我正在尝试使用GNU coreutil top的公式来计算CPU使用率百分比. 但是top使用的是half_total来计算百分比，这是在百分比上加上0.5.

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.

在top的utils.c中来源，下一行(在3.8 beta1版中，其行号为459):-

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);

*out++ = (int)((*diffs++ * 1000 + half_total) / total_change);

这意味着: ((* diffs ++ * 1000)/total_change)+ 1/2 因此，它总是给出一个数字，即:百分比的10倍，再加上0.5".因此，如果百分比是x，它将返回10x + 0.5.

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.

任何人都可以解释该平均值是如何计算的吗?或至少有一些可以从中获得帮助的指针?

Can anyone explain how is this average calculated? or at least some pointer where I can get the help?

PS: 为什么我们不能只使用(*diffs++/total_change) * 100来获得所需的百分比?

PS: Why can't we just use (*diffs++/total_change) * 100 to get the required percentage?

Top的源代码位于:- http://downloads.sourceforge.net/unixtop/top-3.8beta1.tar.gz?modtime=1210117842&big_mirror=0

Top's source code is located at: - http://downloads.sourceforge.net/unixtop/top-3.8beta1.tar.gz?modtime=1210117842&big_mirror=0

推荐答案

这是对整数值进行舍入的方法，因为除法会舍弃小数部分.

This is the way to do rounding for integer values, because the division discards the fractional part.

当您将除数增加一半时，这等于浮点除法，如果小数部分为0.5或更大，则四舍五入.

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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