Messages in this thread | | | Date | Thu, 25 Sep 2008 18:45:53 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [RFC PATCH 1/3] Unified trace buffer |
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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? If you send the same signal to CPU1 that is 1 foot away, as well as send it to CPU2 that is 2 feet away. CPU2 will get that signal at least 1 nanosec after CPU1 receives it.
Of course if the hardware is smart enough to know this topology, then it could account for these delays in traffic.
-- Steve
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