I have submitted https://reviews.freebsd.org/D23376 for avoiding the PowerMac threads-stuck-sleeping issue

[Mark Millard]

I've described my first ever reviews.freebsd.org/D?????
submittal with:

QUOTE
REVISION SUMMARY
 Explicitly initialize the bsp's TB value early on. For PowerMacs with multiple sockets or cores only, have machdep_ap_bootstrap for each ap make a round trip with the bsp to get a current bsp's TB value and then shift the ap's time so that the midpoint of the shifted round tip interval approximately matches the TB value the bsp supplied. The round trips and data transfers use a memory protocol.

 For non-PowerMacs, do the old way for the ap's.

TEST PLAN
 I've been running based on the patches being invovled since late 2019-May or so: PowerMac11,2 with 2 sockets, 2 cores each, and PowerMac3,6 with 2 sockets, 1 core each. No examples of 1 socket with 2 cores, unfortunately. No examples of powerpc64 or powerpc non-PowerMacs either. I do use the same source tree to build for amd64, aarch64, and armv7 and they have been working too. But the patch material is extracted from a source tree that has more local changes: the testing has not been with only these changes.

 I've not had any examples of the stuck-sleeping issue since adopting these changes. Nor have I had new problems from the changes.
END QUOTE


A summary of my changes is:


Part 0:
Avoid interrupts messing up mttb use:

sys/powerpc/include/cpufunc.h


Part 1:
Enable the "alternate_timebase_sync_style" indicator
only for PowerMacs:

sys/powerpc/powermac/platform_powermac.c


Part 2:
The code supporting machdep_ap_bootstrap's part of the
hard work, including the changes to machdep_ap_bootstrap:

sys/powerpc/powerpc/mp_machdep.c


Part 3:
Making sure that the bsp follows the rule:
"The TB is a volatile resource and must be initialized during reset."

sys/powerpc/powerpc/machdep.c




I'll note that I'm not style(9) literate/familiar and at the time
my capacity went to investigating the problem and potential solutions,
not to style(9). So, once a technique is classified as okay, how
it is written in the source would need its own round of work,
presuming my submittal does not inspire a separate fix by someone.

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)