[Lvlug] CentOS runs too fast in vmware
mstanley at technologist.com
Wed Dec 6 22:03:46 EST 2006
I don't know how many of you are running vmware virtual servers but I just ran
into a problem with the system clock running way too fast in CentOS while
running it as a guest operating system. The funny thing is that vmware will
compensate for a slow running clock but not a fast running clock.
I searched all over the place and although there were solutions none of them
worked. There was even a response on vmware's site that said this is an
ongoing problem and they are woking on it.
Well, you are the first to hear this: If you are running CentOS as a guest OS
under vmware you need to disable a service called "irqbalance" by
doing 'chkconfig irqbalance off' and then rebooting CentOS. (You actually
have to reboot because you can't disable the service once it is running.)
Irqbalance is used for spreading irq's across two or more processors and
CentOS will think you have two procs even if it is just using hyperthreading.
The problem is compounded by the 2.6 kernel which uses interrupt requests for
monitoring the system clock. Any 'lost' irq's are corrected for in an
algorithm that tries to compensate by adjust the time accordingly. Since
vmware controls the irq's there are a LOT of them that get lost which causes
the algorithm to accelerate the clock by almost 40%.
Hope that helps someone. What a PITA that was.
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