I have two Ultra 60. Periodically they hard lookup or panic.
	Example:
======================================================================
panic: ipi_send: couldn't send ipi
at line 455 in file /usr/src/sys/sparc64/sparc64/mp_machdep.c
cpuid = 0;
Debugger("panic")
======================================================================

And no "db>" prompt. Sometimes kernel go to DDB. But core dump is not
possible to save.

Fix: Increase IPI_RETRIES to big value???
How-To-Repeat: 	I have included some debug code (see attached patch) into kernel
and increase IPI_RETRIES from 100 to 1000000.
	My code have cyclic array for storing last 32 counters of iteration.
Also it have max_ipi_retries variable for storing maximum value of iteration
counter.

	Boot machine and go to kgdb:

root@bel# gdb -k /usr/obj/usr/src/sys/SUNC3D/kernel.debug /dev/mem
GNU gdb 5.3 (FreeBSD)
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "sparc64-portbld-freebsd5.2"...
panic messages:
---
---
#0  sched_switch (td=0xc03c1288) at /usr/src/sys/kern/sched_ule.c:1186
1186                    cpu_switch(td, newtd);
(kgdb) p max_ipi_retries
$1 = 1
(kgdb) quit

root@bel# ls -laR /
[10 second output skipped]
^C

root@bel# gdb -k /usr/obj/usr/src/sys/SUNC3D/kernel.debug /dev/mem
[...]
(kgdb) p max_ipi_retries
$1 = 2022

Wow! max_ipi_retries in 20 times more than default limit (100).