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    SubjectRe: [PATCH] clocksource: save mult_orig in clocksource_disable()
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    On Fri, 2009-07-31 at 14:18 +0200, Ingo Molnar wrote:
    > * Magnus Damm <magnus.damm@gmail.com> wrote:
    >
    > > On Fri, Jun 19, 2009 at 4:17 AM, john stultz<johnstul@us.ibm.com> wrote:
    > > > On Fri, 2009-06-19 at 00:24 +0900, Magnus Damm wrote:
    > > >> From: Magnus Damm <damm@igel.co.jp>
    > > >>
    > > >> Save clocksource mult_orig in clocksource_disable().
    > > >>
    > > >> To fix the common case where ->enable() does not setup
    > > >> mult, make sure mult_orig is saved in mult on disable.
    > > >>
    > > >> Also add comments to explain why we do this.
    > > >>
    > > >> Signed-off-by: Magnus Damm <damm@igel.co.jp>
    > > >
    > > > Acked-by: John Stultz <johnstul@us.ibm.com>
    > > >
    > > > Thomas, Andrew, please push this for 2.6.31.
    > >
    > > This one is slowly making it's way in I suppose?
    >
    > Btw., what specific issue does this fix? The commit description is
    > generic, there's no bugzilla link and no other information either
    > that could give me an idea about precisely what incarnation of the
    > bug you have hit.

    Magnus' earlier change to mult_orig makes it so mult_orig is written on
    enable, instead of when we register the clocksource. This causes
    problems as enable() might be called multiple times while a system is
    running, where as the register would only happen once.

    If a user switches away from a clocksource and back to a clocksource,
    the mult_orig will no longer be the original mult, as we will over write
    it with an NTP adjusted mult.

    Its a minor detail, but it causes problems when I do NTP testing across
    different clocksources, as the ppm drift factor does not stay constant
    per clocksource.

    This fix makes sure we store mult_orig over mult on disable() so we
    restore the correct value on the next enable().

    thanks
    -john




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