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

From: Suravee Suthikulpanit
Date: Tue Sep 12 2017 - 11:07:55 EST

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
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.


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