Thiago Jung Bauermann [off-list ref] writes:

Hello,

The hypervisor interface to access 24x7 performance counters (which collect
performance information from system power on to system power off) has been
extended in POWER9 adding new fields to the request and result element
structures.

Also, results for some domains now return more than one result element and
those need to be added to get a total count.

The first two patches fix bugs in the existing code. The following 4
patches are code improvements and the last two finally implement support
for the changes in POWER9 described above.

POWER8 systems only support version 1 of the interface, while POWER9
systems only support version 2. I tested these patches on POWER8 to verify
that there are no regressions, and also on POWER9 DD1.

Where is version 2 documented?

And what happens when we boot on a POWER9 in POWER8 compatibility mode?

cheers