xref: /freebsd/cddl/usr.sbin/dwatch/libexec/lock (revision 434283fda99e89af20c3fe95fde427624ae96d04)

# -*- tab-width: 4 -*- ;; Emacs
# vi: set filetype=sh tabstop=8 shiftwidth=8 noexpandtab :: Vi/ViM
############################################################ IDENT(1)
#
# $Title: dwatch(8) module for dtrace_lockstat(4) contention $
# $Copyright: 2026 Devin Teske. All rights reserved. $
#
############################################################ DESCRIPTION
#
# Print kernel lock contention events reported by dtrace_lockstat(4),
# naming the lock, the thread held-off by it, and for how long. Answers
# "the system is slow -- where is it fighting over locks?" The default
# profile watches block events (thread went off-CPU waiting); lock-spin
# watches spin events instead. Contention shorter than a threshold is
# suppressed (default 1 ms; tunable via DWATCH_LOCK_MS in the environment,
# 0 to show everything).
#
############################################################ PROBE

case "$PROFILE" in
lock|lock-block)
	: ${PROBE:=$( echo \
		lockstat:::adaptive-block, \
		lockstat:::lockmgr-block, \
		lockstat:::rw-block, \
		lockstat:::sx-block )} ;;
lock-spin)
	: ${PROBE:=$( echo \
		lockstat:::adaptive-spin, \
		lockstat:::rw-spin, \
		lockstat:::spin-spin, \
		lockstat:::sx-spin, \
		lockstat:::thread-spin )} ;;
lock-adaptive)
	: ${PROBE:=lockstat:::adaptive-block, lockstat:::adaptive-spin} ;;
lock-lockmgr)
	: ${PROBE:=lockstat:::lockmgr-block} ;;
lock-rw)
	: ${PROBE:=lockstat:::rw-block, lockstat:::rw-spin} ;;
lock-sx)
	: ${PROBE:=lockstat:::sx-block, lockstat:::sx-spin} ;;
lock-thread)
	: ${PROBE:=lockstat:::thread-spin} ;;
*)
	: ${PROBE:=lockstat:::${PROFILE#lock-}}
esac

############################################################ EVENT ACTION

: ${DWATCH_LOCK_MS:=1}

case "$DWATCH_LOCK_MS" in
""|*[!0-9]*) die "DWATCH_LOCK_MS must be a number" ;; # NOTREACHED
esac

[ "$CUSTOM_TEST" ] ||
	EVENT_TEST="(int64_t)arg1 >= (int64_t)$DWATCH_LOCK_MS * 1000000"

############################################################ ACTIONS

exec 9<<EOF
this string	lock_class;
this string	lock_how;
this string	lock_name;
this string	lock_verb;

/*
 * Lock classes from sys/lock.h as-witnessed by dtrace_lockstat(4)
 */
inline string lockstat_class[string name] =
	name == "adaptive-block" ?	"mtx" :
	name == "adaptive-spin" ?	"mtx" :
	name == "lockmgr-block" ?	"lockmgr" :
	name == "rw-block" ?		"rw" :
	name == "rw-spin" ?		"rw" :
	name == "spin-spin" ?		"spin mtx" :
	name == "sx-block" ?		"sx" :
	name == "sx-spin" ?		"sx" :
	name == "thread-spin" ?		"thread" :
	name;

inline string lockstat_verb[string name] =
	name == "adaptive-block" ?	"blocked" :
	name == "lockmgr-block" ?	"blocked" :
	name == "rw-block" ?		"blocked" :
	name == "sx-block" ?		"blocked" :
	"spun";

$PROBE /* probe ID $ID */
{${TRACE:+
	printf("<$ID>");
}
	/*
	 * struct lock_object * (first member of every kernel lock)
	 */
	this->lock_name =
		stringof(((struct lock_object *)arg0)->lo_name);
	this->lock_class = lockstat_class[probename];
	this->lock_verb = lockstat_verb[probename];
	this->lock_how = "";
}

lockstat:::lockmgr-block,
lockstat:::rw-block,
lockstat:::sx-block /* probe ID $(( $ID + 1 )) */
{${TRACE:+
	printf("<$(( $ID + 1 ))>");
}
	/* arg2 is 0 when acquiring as writer, 1 as reader */
	this->lock_how = arg2 == 0 ? " as writer" : " as reader";
}
EOF
ACTIONS=$( cat <&9 )
ID=$(( $ID + 2 ))

############################################################ EVENT DETAILS

if [ ! "$CUSTOM_DETAILS" ]; then
exec 9<<EOF
	/*
	 * Print lock contention details
	 */
	printf("%s %d.%03d ms on %s \"%s\"%s",
		this->lock_verb,
		(int64_t)arg1 / 1000000,
		((int64_t)arg1 % 1000000) / 1000,
		this->lock_class,
		this->lock_name,
		this->lock_how);
EOF
EVENT_DETAILS=$( cat <&9 )
fi

################################################################################
# END
################################################################################