funcslower: Make -p switch respect all the process' threads

The -p switch used to set the `set_ftrace_pid` file, which is really
a thread id from the user's perspective. As a result, only the main
thread would be traced. Fix by enumerating the thread ids from /proc/
$pid/task and putting them all in `set_ftrace_pid` when asked.

Signed-off-by: Sasha Goldshtein <goldshtn@gmail.com>

examples/funcslower_example.txt

@@ -101,6 +101,7 @@ USAGE: funcslower [-aChHPt] [-p PID] [-d secs] funcstring latency_us
                  -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
                  -P              # show process names & PIDs
                  -t              # show timestamps
   eg,

kernel/funcslower

@@ -53,19 +53,20 @@
 ### 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_proc=0; opt_time=0; opt_cpu=0
+opt_duration=0; duration=; opt_pid=0; pid=; opt_tid=0; tid=
+pidtext=; opt_headers=0; opt_proc=0; opt_time=0; opt_cpu=0
 trap ':' INT QUIT TERM PIPE HUP	# sends execution to end tracing section
 
 function usage {
 	cat <<-END >&2
-	USAGE: funcslower [-aChHPt] [-p PID] [-d secs] funcstring latency_us
+	USAGE: funcslower [-aChHPt] [-p PID] [-L TID] [-d secs] funcstring latency_us
 	                 -a              # all info (same as -HPt)
 	                 -C              # measure on-CPU time only
 	                 -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
 	                 -P              # show process names & PIDs
 	                 -t              # show timestamps
 	  eg,
@@ -116,13 +117,14 @@ function edie {
 }
 
 ### process options
-while getopts aCd:hHp:Pt opt
+while getopts aCd:hHp:L:Pt opt
 do
 	case $opt in
 	a)	opt_headers=1; opt_proc=1; opt_time=1 ;;
 	C)	opt_cpu=1; ;;
 	d)	opt_duration=1; duration=$OPTARG ;;
 	p)	opt_pid=1; pid=$OPTARG ;;
+    L)  opt_tid=1; tid=$OPTARG ;;
 	H)	opt_headers=1; ;;
 	P)	opt_proc=1; ;;
 	t)	opt_time=1; ;;
@@ -133,10 +135,12 @@ shift $(( $OPTIND - 1 ))
 
 ### option logic
 (( $# < 2 )) && usage
+(( opt_pid && opt_tid )) && edie "ERROR: You can use -p or -L but not both."
 funcs="$1"
 shift
 thresh=$1
 (( opt_pid )) && pidtext=" for PID $pid"
+(( opt_tid )) && pidtext=" for TID $tid"
 printf "Tracing \"$funcs\"$pidtext slower than $thresh us"
 if (( opt_duration )); then
 	echo " for $duration seconds..."
@@ -175,9 +179,18 @@ if ! echo $thresh > tracing_thresh; then
 	edie "ERROR: setting tracing_thresh to $thresh. Exiting."
 fi
 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\" filter. Function exist? Exiting."

man/man8/funcslower.8

@@ -3,7 +3,7 @@
 funcslower \- trace kernel functions slower than a threshold (microseconds). Uses Linux ftrace.
 .SH SYNOPSIS
 .B funcslower
-[\-aChHPt] [\-p PID] [\-d secs] funcstring latency_us
+[\-aChHPt] [\-p PID] [\-L TID] [\-d secs] funcstring latency_us
 .SH DESCRIPTION
 This uses the Linux ftrace function graph profiler to time kernel functions
 and filter them based on a latency threshold. Latency outliers can be studied
@@ -49,6 +49,9 @@ 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
 \-P
 Show process names and process IDs with every line of output.
 .TP