Re: Question about ktime_get_mono_fast_ns() non-monotonic behavior

[Yosry Ahmed]

On Thu, Oct 13, 2022 at 5:03 PM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
>
> On Wed, Oct 12, 2022 at 8:07 PM John Stultz <jstultz@xxxxxxxxxx> wrote:
> >
> > On Wed, Oct 12, 2022 at 8:02 PM John Stultz <jstultz@xxxxxxxxxx> wrote:
> > > On Mon, Sep 26, 2022 at 2:18 PM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
> > > So I think it reasonable to say its bounded by approximately  2 *
> > > NSEC_PER_SEC/HZ +/- 11%.
> >
> > Sorry, this should be 2*NSEC_PER_SEC/HZ * 0.11
>
> Thanks so much for the detailed response :)
>
> IIUC this error bound is in ns. So on a 2 GHz cpu the bound is 0.11 ns
> (essentially 0)? I feel like I miscalculated, this error bound is too
> good to be true.

Never mind, I thought HZ is the cpu speed for some reason. It's the
number of jiffies per second, right?
So if HZ is 1000, the error bound is actually ~2 ms, which is very
large considering that the unit is ns.

Right?

>
> >
> > thanks
> > -john