On Nov 15, 2011, at 1:24 PM, Hans Petter Selasky wrote:
>>
>> ... and I also just remembered that I have seen recommendations that,
>> when FreeBSD is used as a virtual machine, hz should be set to 100 so
>> that the virtual interrupt overhead is reduced. Those two
>> recommendations are at odds with each other.
>
> USB in virtual machines is a completely different story. All the timing
> critical stuff is handled by the real USB host operating system. The OS
> inside
> the VM just has to respond to some "virtual" USB events. Timing does not
kern.hz=100 (!= 1000) recommendation matters because:
1. It causes too many interrupts on multicore systems, which folks reported
caused performance degradation.
2. In VMs it caused clock skew IIRC.
I could dig up sources if you need them.
Thanks,
-Garrett_______________________________________________
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