On Wed, 6 Jan 2016, Prarit Bhargava wrote:
> On 01/06/2016 12:34 PM, Thomas Gleixner wrote:
> > On Wed, 6 Jan 2016, John Stultz wrote:
> >> On Wed, Jan 6, 2016 at 5:00 AM, Prarit Bhargava <pra...@redhat.com> wrote:
> >>> -ktime_t ktime_get_with_offset(enum tk_offsets offs)
> >>> +ktime_t ktime_get_with_offset(enum tk_offsets offs, int trylock)
> >>> {
> >>> struct timekeeper *tk = &tk_core.timekeeper;
> >>> unsigned int seq;
> >>> ktime_t base, *offset = offsets[offs];
> >>> s64 nsecs;
> >>> + unsigned long flags = 0;
> >>> +
> >>> + if (unlikely(!timekeeping_initialized))
> >>> + return ktime_set(0, 0);
> >>>
> >>> WARN_ON(timekeeping_suspended);
> >>>
> >>> + if (trylock && !raw_spin_trylock_irqsave(&timekeeper_lock, flags))
> >>> + return ktime_set(KTIME_MAX, 0);
> >>
> >> Wait.. this doesn't make sense. The timekeeper lock is only for reading.
> >>
> >> What I was suggesting to you off line is to have something that avoids
> >> spinning on the seqcounter should if a bug occurs and we IPI all the
> >> cpus, that we don't deadlock or block any printk messages.
> >
> > We could also extend the fast timekeeper with boot/real/tai extensions and
> > use
> > that for printk. You can use ktime_get_mono_fast_ns() today.
> >
>
> Thanks tglx -- I thought about doing that but was put off by the comments
> in __ktime_get_fast_ns() which point out that we could see backwards time
> stamps. But I see your point -- I could do the same "last_time_stamp" check
> and use "??" in the output.
We talk about single digit nanoseconds here and in the case of a crash/bug we
really do not care about that at all.
Thanks,
tglx
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