Re: [RFC PATCH 1/3] Unified trace buffer

[Jeremy Fitzhardinge]

Steven Rostedt wrote:
> On Fri, 26 Sep 2008, Ingo Molnar wrote:
>   
>> Firstly they need a low-frequency (10khz-100khz) shared clock line 
>> across all CPUs. A single line - and since it's low frequency it could 
>> be overlaid on some existing data line and filtered out. That works 
>> across NUMA nodes as well and physics allows it to be nanosec accurate 
>> up to dozens of meters or so.
>>     
>
> Can this possibly be true? I mean, light travels only one foot every
> nanosecond. Can it really keep nanosecond accuracy up to dozens of  meters 
> away? 

Sure.  NTP keeps machines within 1ms (or better) of each other even
though the network latency is much higher and jittery.

    J

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