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Date: Fri, 19 Aug 2016 17:05:51 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Clark Williams <williams@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Jon Masters <jcm@...hat.com>, Daniel Wagner <wagi@...om.org>, Carsten Emde <C.Emde@...dl.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, John Stultz <john.stultz@...aro.org> Subject: Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer 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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