* Steven Rostedt <[email protected]> wrote:
> > i could imagine the following hardware effects to cause time warps:
> >
> > - the TSC is in fact the 'read counter' method of the local APIC timer
> > hardware. So there can be interactions in theory: programming the APIC
> > timer could impact the TSC and vice versa. There have been CPU
> > erratums in this area in the past.
>
> Could this cause a 2 second drop backwards?
i dont think so.
> > - the TSC itself could have short, temporary warps. I had a box that
> > showed such effects.
>
> Can this be a 2 second warp?
the ones i saw were in the 1000-cycles range.
> My older code first used jiffies as a timer, then I switched to TSC
> and then to APIC timer, and then finally ktimer. ktimer was the first
> to show a backwards get_time.
another thing: the monotonicity check is only in get_ktime_mono(), while
there are other places where a monotonic clock is used, which this check
might miss.
Ingo
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