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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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Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer Peter Zijlstra <peterz@infradead.org> - 2016-08-19 16:10 +0200
  Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer Steven Rostedt <rostedt@goodmis.org> - 2016-08-19 17:00 +0200
    Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer Peter Zijlstra <peterz@infradead.org> - 2016-08-19 17:10 +0200
      Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer John Stultz <john.stultz@linaro.org> - 2016-08-19 18:40 +0200
        Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer Thomas Gleixner <tglx@linutronix.de> - 2016-08-23 11:00 +0200
        Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer Peter Zijlstra <peterz@infradead.org> - 2016-08-23 11:50 +0200

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