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    SubjectRe: [PATCH -mm] clocksource init adjustments (fix bug #7426)
    On Thu, 22 Feb 2007 16:13:02 -0800 john stultz <johnstul@us.ibm.com> wrote:

    > This patch resolves the issue found here:
    > http://bugme.osdl.org/show_bug.cgi?id=7426
    >
    > The basic summary is:
    > Currently we register most of i386/x86_64 clocksources at module_init
    > time. Then we enable clocksource selection at late_initcall time. This
    > causes some problems for drivers that use gettimeofday for init
    > calibration routines (specifically the es1968 driver in this case),
    > where durring module_init, the only clocksource available is the low-res
    > jiffies clocksource. This may cause slight calibration errors, due to
    > the small sampling time used.
    >
    > It should be noted that drivers that require fine grained time may not
    > function on architectures that do not have better then jiffies
    > resolution timekeeping (there are a few). However, this does not
    > discount the reasonable need for such fine-grained timekeeping at init
    > time.
    >
    > Thus the solution here is to register clocksources earlier (ideally when
    > the hardware is being initialized), and then we enable clocksource
    > selection at fs_initcall (before device_initcall).
    >
    > This patch should probably get some testing time in -mm, since
    > clocksource selection is one of the most important issues for correct
    > timekeeping, and I've only been able to test this on a few of my own
    > boxes.

    This doornails my Nocona box early in boot:
    http://userweb.kernel.org/~akpm/s5000431.jpg

    Slab isn't ready yet - time_init()->hpet_arch_init() is called before
    start_kernel() has run kmem_cache_init().


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