On Tue, 26 Feb 2002, Jorge Aldana wrote:
> Why isn't WITNESS and WITNESS_SKIPSPIN in LINT? Or is it undocumented?
> While I'm at it what are they, if you know.
They're in NOTES, the -CURRENT equivilent of LINT. You can build LINT
from NOTES by typing in:
make LINT
in your conf directory.
Here are the entries on those settings:
# SMP Debugging Options:
#
# MUTEX_DEBUG enables various extra assertions in the mutex code.
# WITNESS enables the mutex witness code which detects deadlocks and cycles
# during locking operations.
# WITNESS_DDB causes the witness code to drop into the kernel debugger if
# a lock heirarchy violation occurs or if locks are held when going to
# sleep.
# WITNESS_SKIPSPIN disables the witness checks on spin mutexes.
options MUTEX_DEBUG
options WITNESS
options WITNESS_DDB
options WITNESS_SKIPSPIN
It's worth noting that WITNESS can have a dramatic impact on performance.
I actually turned it off by default recently, and it got turned back on
again (for good reasons). Any benchmarking must be done without those
settings turned on.
Robert N M Watson FreeBSD Core Team, TrustedBSD Project
robert@fledge.watson.org NAI Labs, Safeport Network Services
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