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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [patch V6 01/37] tracing/hwlat: Use ktime_get_mono_fast_ns()
In-Reply-To: <20200520201453.GE325280@hirez.programming.kicks-ass.net>
References: <20200515234547.710474468@linutronix.de> <20200515235124.466962628@linutronix.de> <20200520201453.GE325280@hirez.programming.kicks-ass.net>
Date:   Thu, 21 May 2020 00:20:51 +0200
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Peter Zijlstra <peterz@infradead.org> writes:

> On Sat, May 16, 2020 at 01:45:48AM +0200, Thomas Gleixner wrote:
>> Timestamping in the hardware latency detector uses sched_clock() underneath
>> and depends on CONFIG_GENERIC_SCHED_CLOCK=n because sched clocks from that
>> subsystem are not NMI safe.
>
> AFAICT that's not actually true, see commit:
>
>   1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read from NMI")
>
> that said, no objection to switching to ktime, people that run HPET
> clocks deserve all the pain and suffering available with those setups.

Correct ...