Messages in this thread | | | From | John Stultz <> | Date | Fri, 19 Aug 2016 09:36:41 -0700 | Subject | Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer |
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On Fri, Aug 19, 2016 at 8:05 AM, Peter Zijlstra <peterz@infradead.org> wrote: > 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.
Oof. Apologies. I missed that the fast methods called that helper as well.
Any objection to open-coding it for the fast method, like (sorry for the whitespace damage here):
@@ -401,7 +401,10 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf) do { seq = raw_read_seqcount_latch(&tkf->seq); tkr = tkf->base + (seq & 0x01); - now = ktime_to_ns(tkr->base) + timekeeping_get_ns(tkr); + now = ktime_to_ns(tkr->base); + + now += clocksource_delta(tkr->read(tkr->clock), + tkr->cycle_last, tkr->mask); } while (read_seqcount_retry(&tkf->seq, seq));
return now;
If not I'll get such a patch sorted, tested and tagged for -stable.
thanks -john
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