Re: [PATCH 3/3] KVM: SVM: Add irqchip_split() checks before enabling AVIC

[Suravee Suthikulpanit]

On 9/12/17 07:22, Paolo Bonzini wrote:
> On 12/09/2017 15:17, Radim KrÄmÃÅ wrote:
> > > > Yeah, hacking TMR to get the VM exit could result in future bugs.
> > > > We have to push split irqchip as the deafult in userspaces with this
> > > > change.
> > > Actually, I'm not quite sure about the advantages/disadvantages with split
> > > irqchip, and how it would affect other cases, and why it was not used as
> > > default currently.
> > The main advantage of split irqchip is that we're moving code out of the
> > kernel, and QEMU's irqchip currently has more features too.
> >
> > I think it is not the default as the support for split irqchip is recent
> > (v4.3) and has lower performance, so it is only used in cases that need
> > the extra features.
>
> One other difference is that in-kernel PIT is not supported with
> split-irqchip, and the QEMU PIT lacks support for reinjecting lost
> ticks.  But this should only be needed for very old guests at this point.
>
> Paolo

Thanks. I'll look into patch for changing the default in QEMU and follow up with 
that separately then.

Suravee