[time-nuts] NTP jitter with Linux

Chris Albertson albertson.chris at gmail.com
Thu Apr 5 18:29:01 UTC 2012


On Thu, Apr 5, 2012 at 11:11 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
> My guess on the original question is that keeping the CPU busy puts junk into
> the cache so the whole interrupt processing path takes every possible cache
> miss.

Cache misses are nanosecond level events not tens of microseconds.  If
you see the interrupt hander it is clear that it fits entirely in one
cache line.  However it could be unlucky seattle a foundry and then
two line would need to be loaded.  It's a two level cache so a "miss"
only means going to the secondary which is still very fast.

I think recovering from sleep mode is the most likely explanation.
We STILL don't know the exact make and model CPU so we don't know if
sleep can be disabled.






Chris Albertson
Redondo Beach, California



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