[ntp:questions] best gps receiver for time synchronization
"terje.mathisen at tmsw.no" at ntp.org
Thu Mar 12 10:44:44 UTC 2009
Uwe Klein wrote:
> Kevin Oberman wrote:
>> To get an idea of the fanaticism involved, several years ago, Kirk
>> McKusick and my former boss here in Berkeley counted the machine cycles
>> in the FreeBSD kernel for the PPS response(all done in the interrupt
>> service routine) and used that to correct the time. Of course,in the
>> days of 16 and 40 MHz systems, this was a bit more important.
> Determinism has been lost.
> Cache hits/misses, abitrated bus accesses, multicore contention, ...
> All have cost determinism in latency. You can count cycles
> but wont see the same count ever.
Which is one of the reasons the short pipeline and in-order Pentium made
some pretty nice ntp servers.
This is coming back you know, in the form of Atom and Larrabee cpus:
Many in-order cores with much more deterministic performance.
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
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