Introduce the new kernel thread called "deadlock resolver".

While the name is pretentious, a good explanation of its targets is
reported in this 17 months old presentation e-mail:
http://lists.freebsd.org/pipermail/freebsd-arch/2008-August/008452.html

In order to implement it, the sq_type in sleepqueues is mandatory and not
only compiled along with INVARIANTS option. Additively, a new sleepqueue
function, sleepq_type() is added, returning the type of the sleepqueue
linked to a wchan.
Three new sysctls are added in order to configure the thread:
debug.deadlkres.slptime_threshold
debug.deadlkres.blktime_threshold
debug.deadlkres.sleepfreq

rappresenting the thresholds for sleep and block time that will lead to
a deadlock matching (when exceeded), while the sleepfreq rappresents the
number of seconds between 2 consecutive thread runnings.
In order to enable the deadlock resolver thread recompile your kernel
with the option DEADLKRES.

Reviewed by:	jeff
Tested by:	pho, Giovanni Trematerra
Sponsored by:	Nokia Incorporated, Sandvine Incorporated
MFC after:	2 weeks

1 files changed, 5 insertions, 0 deletions

diff --git a/UPDATING b/UPDATING
index f730b25..8e0ad19 100644
--- a/UPDATING
+++ b/UPDATING
@@ -22,6 +22,11 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 9.x IS SLOW:
 	machines to maximize performance.  (To disable malloc debugging, run
 	ln -s aj /etc/malloc.conf.)
 
+20100108:
+	Introduce the kernel thread "deadlock resolver" (which can be enabled
+	via the DEADLKRES option, see NOTES for more details) and the
+	sleepq_type() function for sleepqueues.
+
 20091202:
 	The rc.firewall and rc.firewall6 were unified, and
 	rc.firewall6 and rc.d/ip6fw were removed.