Re: [PATCH] powerpc/pseries: Use doorbells even if XIVE is available

[ ...  ]

quoted

quoted

An option vector (or dt-cpu-ftrs) could be defined to disable msgsndp
to get KVM performance back.

An option vector would require a PAPR change. Unless the architecture 
reserves some bits for the implementation, but I don't think so. Same
for CAS.

quoted

Qemu/KVM populates /proc/device-tree/hypervisor, so we *could* look at
that. Though adding PowerVM/KVM specific hacks is obviously a very
slippery slope.

QEMU could advertise a property "emulated-msgsndp", or something similar, 
which would be interpreted by Linux as a CPU feature and taken into account 
when doing the IPIs.

This is really a PowerVM optimization. 

The CPU setup for XIVE needs a cleanup also. There is no need to allocate
interrupts for IPIs anymore in that case.

We need to keep these for the other cores. The XIVE layer is unchanged.
 
C.