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    SubjectRe: division and cpu usage

    On Thu, 23 Aug 2007, Luka Napotnik wrote:
    > Hello.
    > I'm new to kernel development and have some questions.
    > 1. Why can't I divide with regular casting to double ((double)a /
    > (double)b)? It gives me strange errors when compiling:
    > WARNING: "__divdf3" [/root....] undefined!
    > WARNING: "__addf3" [/root/...] undefined!
    > WARNING: "__floatsidf" [/root/...] undefined!
    > And if I compile with normal integers, I get zero as the result.
    > 2. I'm trying to get the percentage of CPU used for a certain
    > task_struct and figured the following formula:
    > (task->utime + task->stime) / jiffies
    > Before calculating I convert all the variables to jiffies. Is this correct?
    > Please help.
    > Greets,
    > Lukla

    Floating point operations are not allowed in the kernel. Often,
    when you think you are simply creating a constant, the compiler
    generates runtime code so you have to watch out for that as well.

    You can use "long long" for high precision math if necessary.

    Dick Johnson
    Penguin : Linux version on an i686 machine (5588.30 BogoMips).
    My book :

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