powerpc64 head -r344018 stuck sleeping problems: th->th_scale * tc_delta(th) overflows unsigned 64 bits sometimes [patched failed]

[Ian Lepore]

On Fri, 2019-03-01 at 20:57 +0000, Poul-Henning Kamp wrote:
> --------
> In message <679402FF-907C-43AF-B18C-8C9CC857D7A6 at yahoo.com>, Mark
> Millard via freebsd-hackers writes:
> 
> > > I must admit that 2 seconds of interval where the timehands where
> > > not updated is too much.
> 
> I have no idea how you got in that situation, but it is very far
> from how timecounters were designed to work.
> 

I wonder if it's fallout from reducing the number of timehands to 2,
which always struck me as a really bad idea. I know of at least one arm
configuration which fails because of it (it takes a combo of a single-
core system, and a pps capture driver that uses hardware latching of
the timer and the polling method for reading the latched value; given
all that, at least 4 sets of timehands are needed to avoid losing PPS
events due to generation changes).

-- Ian