Proposed 6.2 em RELEASE patch

Scott Long scottl at
Sun Nov 12 16:42:06 UTC 2006

Mike Tancsa wrote:
> At 01:42 AM 11/11/2006, Scott Long wrote:
> driver.  What will help me is if you can hook up a serial console to
>> your machine and see if it can be made to drop to the debugger while it
>> is under load and otherwise unresponsive.  If you can, getting a process
>> dump might help confirm where each CPU is spending its time.
> ./netblast 500 110 1000
> I compiled in the various debugging options and on the serial console I 
> get a few
> Expensive timeout(9) function: 0xc0601e48(0) 0.024135749 s
> and the serial console

One CPU seems to be stuck in softclock.  My guess here is that there is 
significant lock contention.  Please try the following:

1. Use addr2line or gdb on the kernel to find out what function is at
0xc0601e48 (the address that was printed above).  This address will
change every time you recompile the kernel, so you'll need to reacquire
it from the console each time.
2. Try compiling in WITNESS and running the test as before, then break
into the debugger as before.  Run 'show locks'.  I'm not sure how
fruitful this will be, WITNESS might make it unbearably slow.
3. Turn on MUTEX_PROFILING according to the text in /sys/conf/NOTES and
the man page by the same name.
4. Remove ADAPTIVE_GIANT from your config and retest.  If that doesn't
show a difference, then try setting NO_ADAPTIVE_MUTEXES.



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