diff --git a/examples/functrace_example.txt b/examples/functrace_example.txt
index 5a2f9b9..6db51a4 100644
--- a/examples/functrace_example.txt
+++ b/examples/functrace_example.txt
@@ -325,11 +325,12 @@ and events were missed.
 Use -h to print the USAGE message:
 
 # ./functrace -h
-USAGE: functrace [-hH] [-p PID] [-d secs] funcstring
+USAGE: functrace [-hH] [-p PID] [-L TID] [-d secs] funcstring
                  -d seconds      # trace duration, and use buffers
                  -h              # this usage message
                  -H              # include column headers
                  -p PID          # trace when this pid is on-CPU
+                 -L TID          # trace when this thread is on-CPU
   eg,
        functrace do_nanosleep    # trace the do_nanosleep() function
        functrace '*sleep'        # trace functions ending in "sleep"
diff --git a/kernel/functrace b/kernel/functrace
index 3abf4a0..0736392 100755
--- a/kernel/functrace
+++ b/kernel/functrace
@@ -5,7 +5,7 @@
 #
 # This is a proof of concept using Linux ftrace capabilities on older kernels.
 #
-# USAGE: functrace [-hH] [-p PID] [-d secs] funcstring
+# USAGE: functrace [-hH] [-p PID] [-L TID] [-d secs] funcstring
 #    eg,
 #        functrace '*sleep'	# trace all functions ending in "sleep"
 #
@@ -59,16 +59,18 @@
 ### default variables
 tracing=/sys/kernel/debug/tracing
 flock=/var/tmp/.ftrace-lock
-opt_duration=0; duration=; opt_pid=0; pid=; pidtext=; opt_headers=0
+opt_duration=0; duration=; opt_pid=0; pid=; opt_tid=0; tid=; pidtext=
+opt_headers=0
 trap ':' INT QUIT TERM PIPE HUP	# sends execution to end tracing section
 
 function usage {
 	cat <<-END >&2
-	USAGE: functrace [-hH] [-p PID] [-d secs] funcstring
+	USAGE: functrace [-hH] [-p PID] [-L TID] [-d secs] funcstring
 	                 -d seconds      # trace duration, and use buffers
 	                 -h              # this usage message
 	                 -H              # include column headers
 	                 -p PID          # trace when this pid is on-CPU
+	                 -L TID          # trace when this thread is on-CPU
 	  eg,
 	       functrace do_nanosleep    # trace the do_nanosleep() function
 	       functrace '*sleep'        # trace functions ending in "sleep"
@@ -93,7 +95,7 @@ function end {
 	echo "Ending tracing..." 2>/dev/null
 	cd $tracing
 	warn "echo nop > current_tracer"
-	(( opt_pid )) && warn "echo > set_ftrace_pid"
+	(( opt_pid || opt_tid )) && warn "echo > set_ftrace_pid"
 	warn "echo > set_ftrace_filter"
 	warn "echo > trace"
 	(( wroteflock )) && warn "rm $flock"
@@ -113,11 +115,12 @@ function edie {
 }
 
 ### process options
-while getopts d:hHp: opt
+while getopts d:hHp:L: opt
 do
 	case $opt in
 	d)	opt_duration=1; duration=$OPTARG ;;
 	p)	opt_pid=1; pid=$OPTARG ;;
+	L)	opt_tid=1; tid=$OPTARG ;;
 	H)	opt_headers=1; ;;
 	h|?)	usage ;;
 	esac
@@ -126,8 +129,10 @@ shift $(( $OPTIND - 1 ))
 
 ### option logic
 (( $# == 0 )) && usage
+(( opt_pid && opt_tid )) && edie "ERROR: You can use -p or -L but not both."
 funcs="$1"
 (( opt_pid )) && pidtext=" for PID $pid"
+(( opt_tid )) && pidtext=" for TID $pid"
 if (( opt_duration )); then
 	echo "Tracing \"$funcs\"$pidtext for $duration seconds..."
 else
@@ -148,9 +153,18 @@ sysctl -q kernel.ftrace_enabled=1	# doesn't set exit status
 read mode < current_tracer
 [[ "$mode" != "nop" ]] && edie "ERROR: ftrace active (current_tracer=$mode)"
 if (( opt_pid )); then
-	if ! echo $pid > set_ftrace_pid; then
-		edie "ERROR: setting -p $pid (PID exist?). Exiting."
-	fi
+    echo > set_ftrace_pid
+    # ftrace expects kernel pids, which are thread ids
+    for tid in /proc/$pid/task/*; do
+        if ! echo ${tid##*/} >> set_ftrace_pid; then
+            edie "ERROR: setting -p $pid (PID exist?). Exiting."
+        fi
+    done
+fi
+if (( opt_tid )); then
+    if ! echo $tid > set_ftrace_pid; then
+        edie "ERROR: setting -L $tid (TID exist?). Exiting."
+    fi
 fi
 if ! echo "$funcs" > set_ftrace_filter; then
 	edie "ERROR: enabling \"$funcs\". Exiting."
diff --git a/man/man8/functrace.8 b/man/man8/functrace.8
index a9b9904..bd7f08c 100644
--- a/man/man8/functrace.8
+++ b/man/man8/functrace.8
@@ -3,7 +3,7 @@
 functrace \- trace kernel function calls matching specified wildcards. Uses Linux ftrace.
 .SH SYNOPSIS
 .B functrace
-[\-hH] [\-p PID] [\-d secs] funcstring
+[\-hH] [\-p PID] [\-L TID] [\-d secs] funcstring
 .SH DESCRIPTION
 This tool provides a quick way to capture the execution of kernel functions,
 showing basic details including as the process ID, timestamp, and calling
@@ -45,6 +45,9 @@ Print column headers.
 \-p PID
 Only trace kernel functions when this process ID is on-CPU.
 .TP
+\-L TID
+Only trace kernel functions when this thread ID is on-CPU.
+.TP
 funcstring
 A function name to trace, which may include file glob style wildcards ("*") at
 the beginning or ending of a string only. Eg, "vfs*" means match "vfs" followed