Comment 9 for bug 1761626

I'm not even remotely sure about things here, so some raw notes:

* Current bisect effort ("oh man, this will take forever"):

# bad: [69973b830859bc6529a7a0468ba0d80ee5117826] Linux 4.9
# good: [c8d2bc9bc39ebea8437fd974fdbc21847bb897a3] Linux 4.8
git bisect start 'v4.9' 'v4.8'
# good: [a5af7e1fc69a46f29b977fd4b570e0ac414c2338] rxrpc: Fix loss of PING RESPONSE ACK production due to PING ACKs
git bisect good a5af7e1fc69a46f29b977fd4b570e0ac414c2338
# bad: [a379f71a30dddbd2e7393624e455ce53c87965d1] Merge branch 'akpm' (patches from Andrew)
git bisect bad a379f71a30dddbd2e7393624e455ce53c87965d1

* Found ppc_tm=off, tried it on 4.15.0 generic, works!

* Might be a duplicate of https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1664622 - might be a qemu issue

* 4.15.0 does work on scalingstack bos02 POWER8 KVM xenial xenial hosts (-machine pseries-xenial,accel=kvm,usb=off -cpu host), but I figured that had already been tested and would have been noticed by now. (If I hadn't mentioned before, the host running the ppc64el fullvirt VM at home is a xenial host.)

* See also http://lists.gnu.org/archive/html/qemu-ppc/2018-01/msg00021.html - might be mitigated with pseries-2.12 with a bionic host qemu setup, but I don't have an easy way to test with a bionic host + qemu at the moment.