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profiling broken on MP systems?
We've been trying to do some profiling on a system which is a
dual-processor x86 running NetBSD/i386 5.1.
It has not gone well. If we enable profiling for more than 0.2 seconds,
the system locks up. Even more distressingly, sometimes attempts to
turn off profiling simply don't: kgmon -h reports that it turned off
profiling, but actually it didn't. To quote one of my coworkers:
> .2 seconds was fine. .3 was not. Even though it claimed to have turned
> profiling off, profiling was actually still on.
> I broke into the debugger and _gmonparam was 0: GMON_PROF_ON. Manually
> patching it to 3 in my debugger curiously did not work. It kept being set
> to 0.
> With DDB write command, I was able to set it to 3, and after a while, the
> system came back and I was able to obtain the trace.
Another disturbing effect we've noticed is that the sysmon sme_worker goes
crazy when profiling is turned on: it appears to loop sending cv_broadcast()
a million times, and to be scheduled every few ticks instead of once every
30 seconds. I cannot account for why this would be by (quick) code
examination. Unfortunately disabling it does not solve the system hangs
when we turn on profiling on the MP kernel, however.
The only even remotely unusual thing about our kernel is that it's built
with HZ=1024. We have confirmed that hz = profhz = stathz = 1024 at runtime,
Does anyone have profiling working on a multiprocessor system right now?
On i386? With netbsd-5?
Thor Lancelot Simon
"We cannot usually in social life pursue a single value or a single moral
aim, untroubled by the need to compromise with others." - H.L.A. Hart
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