On 12/09/2017 15:17, Radim Krčmář 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
