Messages in this thread | | | Date | Fri, 19 Aug 2016 17:05:51 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer |
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On Fri, Aug 19, 2016 at 10:26:20AM -0400, Steven Rostedt wrote: > > In any case, for those you could probably use ktime_get_mono_fast_ns(). > > Is that safe to call from NMI?
It should be, we were very careful to make it so. Also read the comment with __ktime_get_fast_ns().
> Looking into the code I see: > > now = ktime_to_ns(tkr->base) + timekeeping_get_ns(tkr); > > where timekeeping_get_ns() has: > > timekeeping_get_delta() > > which does: > > read_seqcount_begin() > > which has (eventually):
That's a bug in CONFIG_DEBUG_TIMEKEEPING, if you look at the !timekeeping_get_delta() it does no such thing.
John, looks like 4ca22c2648f9 ("timekeeping: Add warnings when overflows or underflows are observed") buggered things.
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