Re: timekeeping_adjust may set mult to 0

From: John Stultz
Date: Fri Feb 15 2013 - 17:34:40 EST

On Mon, Feb 11, 2013 at 7:48 AM, David Engraf <david.engraf@xxxxxxxxx> wrote:
> I have encountered a problem when a linux system uses a clocksource with
> mult = 1 and shift = 0 (clocksource cycle = nanoseconds). It may happen that
> the function timekeeping_adjust reduces the value of mult to 0 when error is
> lower than the interval [1].
> As soon as timekeeper.mult is 0, ktime_get will no longer work because it
> uses timekeeping_get_ns which converts the cycle to nanoseconds with mult as
> 0 and the system clocksource returns always 0.

So you *don't* want to use shift=0, since that kills the ability for
the frequency adjustment code to do anything, as you've found.

Instead of calculating the clocksource mult/shift pair yourself,
please use clocksource_register_hz/khz().

I'm hoping to kill off the open clocksource_register() call soon, to
avoid this sort of confusion. Sorry for the trouble.

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