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    SubjectRe: [PATCH]: fix 32bits integer overflow in loops_per_jiffy calculation
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    On Thu, 2002-08-22 at 19:46, Dominik Brodowski wrote:
    > On Thu, Aug 22, 2002 at 09:35:16PM +0200, Benjamin Herrenschmidt wrote:
    > > >IMHO per-arch functions are really not needed. The only architectures which
    > > >have CPUFreq drivers by now are ARM and i386. This will change, hopefully;
    > > >IMHO it should be enough to include some basic limit checking in
    > > >cpufreq_scale().
    > >
    > > In this specific case, we were talking about PPC since the problem
    > > occured when I implemented cpufreq support to switch the speed
    > > of the latest powerbooks between 667 and 800Mhz
    >
    > And the patch from Yoann solves this?

    Yep, the integer overflow resulted in an incorrectly computed
    loops_per_jiffy :

    Aug 21 19:50:41 titane kernel: adjust_jiffies: prechange cur=667000, new=800000
    Aug 21 19:50:41 titane kernel: old loop_per_jiffy = 665.19 (cpufreq_ref_loops=3325952, cpufreq_ref_freq=667000).
    Aug 21 19:50:41 titane kernel: new loop_per_jiffy = 669.02 (cpufreq_ref_loops=3325952, cpufreq_ref_freq=667000).

    With the patch applied, it work fine :

    Aug 22 11:33:40 titane kernel: adjust_jiffies: prechange cur=667000, new=800000
    Aug 22 11:33:40 titane kernel: old loop_per_jiffy = 665.19 (cpufreq_ref_loops=3325952, cpufreq_ref_freq=667000).
    Aug 22 11:33:40 titane kernel: new loop_per_jiffy = 797.82 (cpufreq_ref_loops=3325952, cpufreq_ref_freq=667000).

    --
    Yoann Vandoorselaere, http://www.prelude-ids.org

    "Programming is a race between programmers, who try and make more and
    more idiot-proof software, and universe, which produces more and more
    remarkable idiots. Until now, universe leads the race" -- R. Cook

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