Re: kern/53016: Clock not stable

[Tero Kivinen <kivinen%iki.fi@localhost>]

Joerg Sonnenberger writes:
>  Can you also run some background load, main() { for (;;) ; } or so in
>  the background to rule out whether it is deep sleep? Enough instances,
>  even with nice 20, to just keep all cores busy.

When running some tests earlier, I noticed that if I run

dnssec-signzone -N INCREMENT iki.fi

in a loop, I can get the clock drift to happen more often. It is also
easy to see that the drift happened, as the time command normally
reports:

u:11.19s s:0.01s r:3.37s 331%

but in this case the user cpu time was still same (11 seconds), but
real time was only 1.6 seconds instead of 3.4 seconds and cpu usage %
was around 700%, even though the machine only has 4 cores...

So I do not think this is actually going to the any kind of sleep
state, as dnssec-signzone actually uses all cores with full 100% cpu.

I tried to see if running busy loops (like you suggested with just
for(;;); in them) could cause issues, but that didn't affect anything.
Next I tried to busy loop doing fpu operations (for(d=0.0; d <
9.0e20;d += 0.00001);) but no difference there, so it might that
dnssec-signzone does some crypto operations or more complicated fpu
operations that cause this issue to happen. 
-- 
kivinen%iki.fi@localhost