Zitat von Ask Bjørn Hansen <[email protected]>:
On Jul 20, 2015, at 12:29 AM, [email protected] wrote:
The problem with virtualization is not that it doesn't work at all,
but you can never be sure. If you have dedicated hardware you are
able to monopolize CPU to do very accurate counting/timing
operations, […]
But for most actually deployed servers isn’t that almost as true
when you’re not virtualized? Modern kernels and CPUs do all sorts of
tricks to save power and divide resources. Most servers aren’t
configured to run at full speed just in case it makes the time
keeping better.
Ask
That's the problem, it is already difficult to get a precise time
tick/measurement on bare hardware, but with a Hypervisor in between
which is trying to isolate the hardware from the VMs running, it get
worse in some cases because the VMs are not aware of the decisions a
Hypervisor does to manage hardware/counter access. This is *never* a
problem with "standard" use cases but it might get a problem with many
VMs all trying to get reliable time ticks for example.
There are some internals here:
https://www.kernel.org/doc/Documentation/virtual/kvm/timekeeping.txt
But as already said i doubt this is a *real* problem for pool members,
maybe Stratum 1 should care but that is more of a question targeting
the NTP developers i guess.
Regards
Andreas
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