Re: [PATCH v1] watchdog: Use a reference cycle counter to avoid scaling issues

[Andi Kleen]

> We can just detect the deviation in the callback itself:
> 
>        u64 now = ktime_get_mono_fast_ns();
> 
>        if (now - __this_cpu_read(nmi_timestamp) < period)
>        	       return;
> 
>        __this_cpu_write(nmi_timestamp, now);
> 
> It's that simple.

It's a simple short term hac^wsolution. But if we had a (hypothetical) system with
let's say 10*TSC max you may end up with quite a few false ticks, as in 
unnecessary interrupts. With 100*TSC it would be really bad.

There were systems in the past that ran TSC at a much slower frequency,
such as the early AMD Barcelona systems.

So the problem may eventually come back if not solved properly.

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only
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