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

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In message <[email protected]>, Konstantin Belousov writes:

>Using more than two timehands increases a chance of reader to try to
>use outdated timehands.

No, using only two timehands increase the chance that the reader tries
to use the timehand which is being updated.

As long as the reader does not use the timehand being updated, using
a one or two generations old timehand is OK.

At worst a frequency change happened since then, in which case the
timestamp will be "delta-f * delta-t" wrong.  Delta-f is in 1e-7
territory on a system running ntpd(8), so this is below noise level
for anything but high-precision timekeeping.

The target-value for delta-t was "a few milliseconds" when I wrote
timecounters, if somebody has changed that since, I hope they did
their math first.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
[email protected]         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.
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