Re: time warps, I despair

Ingo Molnar (
Thu, 31 Oct 1996 10:18:27 +0100 (MET)

On Thu, 31 Oct 1996, Ulrich Windl wrote:

> I'm working on the Linux clock code. Some long time ago I experienced
> odd time warps I could not explain, and nobody else had a good idea,
> except that the Linux kernel was broken.

this bug was fixed in 2.0.9. Note that we already had the Code Freeze
then, so the code isnt exactly pretty.

It doesnt prevent time warps called from interrupt handlers, more planned
for 2.1. [there are two device writers who wanted to use gettimeoffset()
from interrupt handlers, and i guess the IPV6 code needs such stuff too
... maybe :)]. I'm holding on with the patches until things around
exception handling calm down?

i have a smallish test program that tests >user-space< time warps.

> Now I examined all the code, especially the NTP specific parts I
> validated twice, but found nothing. Then I began to comment-out all
> suspicious parts that might cause it (e.g. updating the CMOS clock).
> Still no success. I suspect some code outside of the timing code, or
> maybe still the Pentium fast timeoffset.

You are calling it from an interrupt handler, right? Thats definitely
unsafe ... was thinking about ways to fix it in 2.0, but all solutions
were just too ugly.

But for 2.1 now it seems that it should be fixed.

-- mingo