Re: timekeeping_adjust may set mult to 0

From: David Engraf
Date: Tue Feb 26 2013 - 08:05:19 EST

Am 15.02.2013 23:34, schrieb John Stultz:
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.

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.


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