Re: infinite loop in read_hpet from ktime_get_boot_fast_ns

Peter Zijlstra
2019-06-12T09:03:15Z

On Tue, Jun 11, 2019 at 11:09:20PM +0200, Thomas Gleixner wrote:
> Jason,
>
> On Fri, 7 Jun 2019, Jason A. Donenfeld wrote:
>
> Adding a few more people on cc and keeping full context.
>
> > Hey Thomas,
> >
> > After some discussions here prior about the different clocks
> > available, WireGuard uses ktime_get_boot_fast_ns() pretty extensively.
> > The requirement is for a quasi-accurate monotonic counter that takes
> > into account sleep time, and this seems to fit the bill pretty well.

How quasi? Do the comments in kernel/sched/clock.c look like something
you could use?

As already mentioned in the other tasks, anything ktime will be
horrifically crap when it ends up using the HPET, the code in
kernel/sched/clock.c is a best effort to keep using TSC even when it is
deemed unusable for timekeeping.