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

Srivatsa Vaddagiri
2010-12-03T16:27:40Z

On Fri, Dec 03, 2010 at 05:27:52PM +0530, Srivatsa Vaddagiri wrote:
> On Thu, Dec 02, 2010 at 11:14:16AM -0800, Chris Wright wrote:
> > 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.
>
> That's not sufficient. Lets we have 3 guests A, B, C that need to be rate
> limited to 25% on a single cpu system. We create this idle guest D that is 100%
> cpu hog as per above definition. Now when one of the guest is idle, what ensures
> that the idle cycles of A is given only to D and not partly to B/C?

To tackle this problem, I was thinking of having a fill-thread associated with
each vcpu (i.e both belong to same cgroup). Fill-thread consumes idle cycles
left by vcpu, but otherwise doesn't compete with it for cycles.

- vatsa