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

Chris Wright
2010-12-03T17:29:32Z

* Srivatsa Vaddagiri (vatsa@linux.vnet.ibm.com) wrote:
> 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.

That's what Marcelo's suggestion does w/out a fill thread.