Messages in this thread | | | Date | Tue, 26 Feb 2013 14:05:05 +0100 | From | David Engraf <> | Subject | Re: timekeeping_adjust may set mult to 0 |
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Am 15.02.2013 23:34, schrieb John Stultz: > On Mon, Feb 11, 2013 at 7:48 AM, David Engraf <david.engraf@sysgo.com> 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.
The problem is not shift=0 it's mult=1. The frequency adjustment code may increase/decrease mult and mult=0 will not work.
> Instead of calculating the clocksource mult/shift pair yourself, > please use clocksource_register_hz/khz().
Thanks, I will try it.
Best regards - David
> I'm hoping to kill off the open clocksource_register() call soon, to > avoid this sort of confusion. Sorry for the trouble. > > thanks > -john >
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