Re: [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v2)

Chris Wright
2010-12-02T19:14:35Z

* Anthony Liguori (aliguori@us.ibm.com) wrote:
> In certain use-cases, we want to allocate guests fixed time slices where idle
> guest cycles leave the machine idling. There are many approaches to achieve
> this but the most direct is to simply avoid trapping the HLT instruction which
> lets the guest directly execute the instruction putting the processor to sleep.

I like the idea, esp to keep from burning power.

> Introduce this as a module-level option for kvm-vmx.ko since if you do this
> for one guest, you probably want to do it for all. A similar option is possible
> for AMD but I don't have easy access to AMD test hardware.

Perhaps it should be a VM level option. And then invert the notion.
Create one idle domain w/out hlt trap. Give that VM a vcpu per pcpu
(pin in place probably). And have that VM do nothing other than hlt.
Then it's always runnable according to scheduler, and can "consume" the
extra work that CFS wants to give away.

What do you think?

thanks,
-chris