It all looks pretty good otherwise. I do worry about POWER8/9 which
do not have BHRB disable bit. How much do they slow down I wonder?
That is a good question! I'll see if I can get some linux boot times
with and without the changes on P9.
I ran some tests booting ubuntu 20.04 on the powrnv9 model and found
that it took about 5% longer to boot to the login prompt with the
changes than without. As discussed offline, I'll remove this support
from P8/P9 as the 5% reduction in performance is not worth the added
functionality. We could perhaps add it back in the future with a
command line option that has it disabled by default on P8/P9.
P10 and on has it disabled for non problem state branches, so we
should be good there.
Thanks,
Glenn
