[CentOS] vmware-time update issues and typematic issues

Aleksandar Milivojevic alex at milivojevic.org
Sat Sep 23 12:26:41 UTC 2006

rado wrote:
> right now system times are off 2 mins after all nite ...yest. that would
> have been 10-12hrs. I stopped all ntp or whatever that is...going out to
> one of the time servers...just getting time from the host system.

Some hints from the vmware website for 2.6 kernels say to use 
"clock=pit" kernel option in guests, disable NTP in guests (system 
clocks in virtual machines are too unstable), and let vmware tools sync 
the time with the host OS (you can use NTP to sync the time of the host 
OS with some time source, of course).

If you have both 2.4 and 2.6 kernels running in guests, you'll probably 
notice that 2.6 kernels are taking 3-4 times more CPU time when the 
guest is idling.  That's because the default frequency of interrupts 
changed from 100Hz to 1kHz (and that is per CPU) in 2.6 kernels. 
Placing much more stress on vmware and causing all bunch of problems 
with it.  It's configurable compile time option (you'd need to recompile 
kernel to change it to the old default).  I have one (not really brand 
new anymore) dual-Xeon machine that runs ESX with 5 2.6 guests and 
couple of 2.4 guests.  When all the guests are idle, they consume about 
half of the CPU time of one processor.  I haven't yet attempted 
recompiling 2.6 kernel and lowering frequency of interrupts, but it's 
probably worth trying.

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