lkml.org 
[lkml]   [2022]   [Oct]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: Question about ktime_get_mono_fast_ns() non-monotonic behavior
On Thu, Oct 13, 2022 at 6:29 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> On Thu, Oct 13, 2022 at 5:03 PM Yosry Ahmed <yosryahmed@google.com> wrote:
> >
> > On Wed, Oct 12, 2022 at 8:07 PM John Stultz <jstultz@google.com> wrote:
> > >
> > > On Wed, Oct 12, 2022 at 8:02 PM John Stultz <jstultz@google.com> wrote:
> > > > On Mon, Sep 26, 2022 at 2:18 PM Yosry Ahmed <yosryahmed@google.com> 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?

Correct.

> So if HZ is 1000, the error bound is actually ~2 ms, which is very
> large considering that the unit is ns.

Uh, for HZ=1000, I think it's closer to 220us, but yes, for HZ=100 2.2ms.

thanks
-john

\
 
 \ /
  Last update: 2022-10-14 04:16    [W:0.763 / U:0.836 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site