Re: [PATCH RFC V4 5/5] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock

[Marcelo Tosatti <mtosatti@xxxxxxxxxx>]

On Tue, Jan 17, 2012 at 05:32:33PM +0200, Gleb Natapov wrote:
> On Tue, Jan 17, 2012 at 07:58:18PM +0530, Srivatsa Vaddagiri wrote:
> > * Gleb Natapov <gleb@xxxxxxxxxx> [2012-01-17 15:20:51]:
> > 
> > > > Having the hypercall makes the intent of vcpu (to sleep on a kick) clear to 
> > > > hypervisor vs assuming that because of a trapped HLT instruction (which
> > > > will anyway won't work when yield_on_hlt=0).
> > > > 
> > > The purpose of yield_on_hlt=0 is to allow VCPU to occupy CPU for the
> > > entire time slice no mater what. I do not think disabling yield on HLT
> > > is even make sense in CPU oversubscribe scenario.
> > 
> > Yes, so is there any real use for yield_on_hlt=0? I believe Anthony
> > initially added it as a way to implement CPU bandwidth capping for VMs,
> > which would ensure that busy VMs don't eat into cycles meant for a idle
> > VM. Now that we have proper support in scheduler for CPU bandwidth capping, is 
> > there any real world use for yield_on_hlt=0? If not, deprecate it?
> > 
> I was against adding it in the first place, so if IBM no longer needs it
> I am for removing it ASAP.

+1.

Anthony?

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