[ntp:questions] Leap second bug?

Unruh unruh-spam at physics.ubc.ca
Sun Jan 6 18:03:00 UTC 2008


david at ex.djwhome.demon.co.uk.invalid (David Woolley) writes:

>In article <jFUfj.46999$UZ4.38415 at edtnps89>,
>Unruh <unruh-spam at physics.ubc.ca> wrote:


>> I hope you mean 4 or 10usec, not msec.

>No.  I mean milli-seconds, i.e. 1/HZ for HZ = 100 and 250.

>I've personally had lost clock interrupts due to a disk driver, on Linux,
>at HZ=100, but that was an obsolete high speed interface, on a relatively

Is the timer interupt edge or level triggered? Ie, does this really mean
that the interrupt was turned off for 4 or 10msec, or just that when the
interrupt occured, it was not serviced?
I have not seen anything like that in my system, but It is possible it is
not heavily enough used. I see offsets fluctuations from the ps of 3us
standard deviation, 

 
>slow machine.  People regularly get lost ticks on Linux at HZ=1000, when
>using IDE's in non-DMA mode and I also believe they get them at HZ=250.
>I believe there have been reports at HZ=100.

>Windows users also report lost interrupts, although I'm not 100% sure
>whether that applies with the normal HZ=~64 rate or with the, higher,
>multimedia rate, which might be instigated by other software, although
>ntpd now tends to instigate it itself, to avoid glitches when the rate
>changes.

>One of the problems is that modern operating system kernels tend to
>be written in high level languages, so coders don't cycle count their
>interrupt routines and proper use of priority interrupts can be difficult.
>Short interrupt routines tend not to re-enable higher priorities at all,
>although those won't have the sort of latency given above.




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