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    SubjectRe: [RFC PATCH] x86:Use cpu_khz for loops_per_jiffy calculation
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    On Thu, 2008-06-26 at 10:35 -0700, Pavel Machek wrote:
    > On Thu 2008-06-26 10:20:31, Alok Kataria wrote:
    > > On Tue, 2008-06-24 at 10:57 -0700, Pavel Machek wrote:
    > > > Hi!
    > > >
    > > > > On X86 platform we can use the value of tsc_khz computed during tsc calibration
    > > > > to calculate the loops_per_jiffy value. Its very important to keep the error in
    > > > > lpj values to minimum as any error in that may result in kernel panic in
    > > > > check_timer.
    > > > > In virtualization environment, On a highly overloaded host the guest delay
    > > > > calibration may sometimes result in errors beyond the ~50% that timer_irq_works
    > > > > can handle, resulting in the guest panicking.
    > > >
    > > > How did you adress 'khz has nothing to do with loops per jiffie'
    > > > comment?
    > > >
    > > > Some cpus can do loop in cycle , some need two cycles, some need half.
    > >
    > > Hi Pavel,
    > >
    > > When you say loops per jiffies has nothing to do with khz, by khz you
    > > mean the cpu frequency, right ?
    >
    > Yes.
    >
    > > AFAIU in calibrate_delay_direct too we measure the amount by which timer
    > > has ticked until DELAY_CALIBRATION_TICKS amount of jiffies has passed.
    > > So IMO the code there too assumes that there is one loop per timer
    > > cycle ?
    >
    > On my machine, it reports:
    >
    > delay using timer specific routine.. 3661.98 BogoMIPS (lpj=7323971)
    > ...
    > Detected 1828.828 MHz processor.
    >
    > (/proc/cpuinfo)
    > model name : Genuine Intel(R) CPU T2400 @ 1.83GHz
    > ...
    > cpu MHz : 1000.000
    How is it 1000 here ? shouldn't this be 1830.xx
    > ...
    > bogomips : 3657.54
    >
    > So you'd break it by setting lpj (aka bogomips) to cpu_khz, right?

    We are not setting it to cpu_khz but to tsc_khz, i am assuming that in
    this case tsc_khz will be different than cpu_khz. Can you please mail me
    the full dmesg log.

    Thanks,
    Alok
    >
    > Pavel
    > --
    > (english) http://www.livejournal.com/~pavelmachek
    > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html



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