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    SubjectRe: [patch] sched: accurate user accounting
    On Sunday 25 March 2007 21:34, malc wrote:
    > On Sun, 25 Mar 2007, Ingo Molnar wrote:
    > > * Con Kolivas <> wrote:
    > >> For an rsdl 0.33 patched kernel. Comments? Overhead worth it?
    > >
    > > we want to do this - and we should do this to the vanilla scheduler
    > > first and check the results. I've back-merged the patch to before RSDL
    > > and have tested it - find the patch below. Vale, could you try this
    > > patch against a 2.6.21-rc4-ish kernel and re-test your testcase?
    > [..snip..]
    > Compilation failed with:
    > kernel/built-in.o(.sched.text+0x564): more undefined references to
    > `__udivdi3' follow
    > $ gcc --version | head -1
    > gcc (GCC) 3.4.6
    > $ cat /proc/cpuinfo | grep cpu
    > cpu : 7447A, altivec supported
    > Can't say i really understand why 64bit arithmetics suddenly became an
    > issue here.

    Probably due to use of:

    #define NS_TO_JIFFIES(TIME) ((TIME) / (1000000000 / HZ))
    #define JIFFIES_TO_NS(TIME) ((TIME) * (1000000000 / HZ))

    Excuse our 64bit world while we strive to correct our 32bit blindness and fix
    this bug.

    > Am i supposed to run the testcase and see if numbers in `/proc/stat'
    > now match the reality closer? To be really accurate `/proc/stat'
    > should be left alone methinks, because no matter how good you try the
    > fundamential fact that time(and consequently load percentage) is not
    > really devided in USER_HZ intervals will interfere with ones quest for
    > accurate statistics. (Wonder what this patch will do to slightly modified
    > hog that produced this:
    > but this will have to wait till i get to the PC at work)

    It should far more accurately represent the cpu usage without any userspace

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