[ntp:questions] Which version of Linux works best?
Terje Mathisen
"terje.mathisen at tmsw.no" at ntp.org
Fri Mar 12 09:25:36 UTC 2010
David Woolley wrote:
>> So? The interrupt still takes the same time to be activated. On a GHZ
>> system, there is enough time in 1usec to run 1000 commands, and it is
>> hard to imagine that many being used to return the ioctl. I have worried
>
> That's 1000 machine cycles, not 1000 instructions. On modern systems,
> I'm not sure that 1000 cycles isn't a typical time for a system call on
> modern, high level language progammed, bloatware. (I seem to remember
> hand coding an ISR in assembler to a budget of 100 instructions (for
> 68000) and it not being that easy.)
Interrupt times are quite often in the multi-K cycle count for modern
operating systems. :-(
For ntp it is the variability that really counts, a constant response
time will just lead to a small but fixed offset from the true time. If
you really care you can fudge away that offset. :-)
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
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