On Friday 07 March 2008, John J. Foster wrote:
> Switching to 250Hz looks like it has solved the problem. No time lost
> for a little over an hour now, and ntp is syncing properly, I think.
> But my reading of the help on this setting led me to believe that
> 1000Hz was right for a desktop system.
More like "we think that 1000Hz *should* work better than 250Hz, but we
don't really know for sure and YMMV..."
> Can any explain what this setting actually does, and why it works
> now?
From /usr/src/linux/kernel/Kconfig.hz:
Allows the configuration of the timer frequency. It is
customary
to have the timer interrupt run at 1000 Hz but 100 Hz may be
more
beneficial for servers and NUMA systems that do not need to
have
a fast response for user interaction and that may experience
bus
contention and cacheline bounces as a result of timer
interrupts.
Note that the timer interrupt occurs on each processor in an
SMP
environment leading to NR_CPUS * HZ number of timer interrupts
per second.
The timer wakes up x times per second and demands that it get attention.
Your VM however, cannot control this on the host and the guest kernel
interacts in strange ways with the host kernel.
Just for interest, what are the Hz settings on host and guest?
--
Alan McKinnon
alan dot mckinnon at gmail dot com
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