#!/bin/bash
#
# funcslower - trace kernel functions slower than a threshold (microseconds).
#              Uses Linux ftrace.
#
# This uses the Linux ftrace function graph profiler to time kernel functions
# and filter them based on a latency threshold. This is a proof of concept using
# Linux ftrace capabilities on older kernels.
#
# USAGE: funcslower [-aChHPt] [-p PID] [-d secs] funcstring latency_us
#
# Run "funcslower -h" for full usage.
#
# REQUIREMENTS: FTRACE function graph, which you may already have available
# and enabled in recent kernels. And awk.
#
# The output format is the same as the ftrace function graph trace format,
# described in the kernel source under Documentation/trace/ftrace.txt.
# Note that the output may be shuffled when different CPU buffers are read;
# check the CPU column for changes, or include timestamps (-t) and post sort.
#
# WARNING: This uses dynamic tracing of kernel functions, and could cause
# kernel panics or freezes. Test, and know what you are doing, before use.
#
# OVERHEADS: Timing and filtering is performed in-kernel context, costing
# lower overheads than post-processing in user space. If you trace frequent
# events (eg, pick a common function and a low threshold), you might want to
# try the "-d secs" option, which buffers events in-kernel instead of printing
# them live.
#
# From perf-tools: https://github.com/brendangregg/perf-tools
#
# COPYRIGHT: Copyright (c) 2014 Brendan Gregg.
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU General Public License
#  as published by the Free Software Foundation; either version 2
#  of the License, or (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software Foundation,
#  Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
#
#  (http://www.gnu.org/copyleft/gpl.html)
#
# 12-Jul-2014	Brendan Gregg	Created this.

### default variables
setglobal tracing = '/sys/kernel/debug/tracing'
setglobal flock = '/var/tmp/.ftrace-lock'
setglobal opt_duration = '0'; setglobal duration = ''; setglobal opt_pid = '0'; setglobal pid = ''; setglobal opt_tid = '0'; setglobal tid = ''
setglobal pidtext = ''; setglobal opt_headers = '0'; setglobal opt_proc = '0'; setglobal opt_time = '0'; setglobal opt_cpu = '0'
trap ':' INT QUIT TERM PIPE HUP	# sends execution to end tracing section

proc usage {
	cat <<-END >&2
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,
       funcslower vfs_read 10000 # trace vfs_read() slower than 10 ms

See the man page and example file for more info.
END
	exit
}

proc warn {
	if ! eval @ARGV {
		echo >&2 "WARNING: command failed \"$ifsjoin(ARGV)\""
	}
}

proc end {
	# disable tracing
	echo 2>/dev/null
	echo "Ending tracing..." 2>/dev/null
	cd $tracing

	sh-expr ' opt_time )'&& warn "echo nofuncgraph-abstime > trace_options"
	sh-expr ' opt_proc )'&& warn "echo nofuncgraph-proc > trace_options"
	sh-expr ' opt_cpu )'&& warn "echo sleep-time > trace_options"

	warn "echo nop > current_tracer"
	sh-expr ' opt_pid )'&& warn "echo > set_ftrace_pid"
	warn "echo > set_ftrace_filter"
	warn "echo > set_graph_function"
	warn "echo 0 > tracing_thresh"
	warn "echo > trace"

	sh-expr ' wroteflock )'&& warn "rm $flock"
}

proc die {
	echo >&2 @ARGV
	exit 1
}

proc edie {
	# die with a quiet end()
	echo >&2 @ARGV
	exec >/dev/null 2>&1
	end
	exit 1
}

### process options
while getopts aCd:hHp:L:Pt opt
{
	match $opt {
	with a	setglobal opt_headers = '1'; setglobal opt_proc = '1'; setglobal opt_time = '1' 
	with C	setglobal opt_cpu = '1'; 
	with d	setglobal opt_duration = '1'; setglobal duration = $OPTARG 
	with p	setglobal opt_pid = '1'; setglobal pid = $OPTARG 
    with L  setglobal opt_tid = '1'; setglobal tid = $OPTARG 
	with H	setglobal opt_headers = '1'; 
	with P	setglobal opt_proc = '1'; 
	with t	setglobal opt_time = '1'; 
	with h|?	usage 
	}
}
shift $shExpr(' $OPTIND - 1 ')

### option logic
sh-expr ' $# < 2 )'&& usage
sh-expr ' opt_pid && opt_tid )'&& edie "ERROR: You can use -p or -L but not both."
setglobal funcs = $1
shift
setglobal thresh = $1
sh-expr ' opt_pid )'&& setglobal pidtext = "" for PID $pid""
sh-expr ' opt_tid )'&& setglobal pidtext = "" for TID $tid""
printf "Tracing \"$funcs\"$pidtext slower than $thresh us"
if sh-expr ' opt_duration ' {
	echo " for $duration seconds..."
} else {
	echo "... Ctrl-C to end."
}

## select awk
if sh-expr ' opt_duration ' {
	[[ -x /usr/bin/mawk ]] && setglobal awk = 'mawk' || setglobal awk = 'awk'
} else {
	# workarounds for mawk/gawk fflush behavior
	if [[ -x /usr/bin/gawk ]] {
		setglobal awk = 'gawk'
	} elif [[ -x /usr/bin/mawk ]] {
		setglobal awk = '"mawk -W interactive'"
	} else {
		setglobal awk = 'awk'
	}
}

### check permissions
cd $tracing || die "ERROR: accessing tracing. Root user? Kernel has FTRACE?
    debugfs mounted? (mount -t debugfs debugfs /sys/kernel/debug)"

### ftrace lock
[[ -e $flock ]] && die "ERROR: ftrace may be in use by PID $[cat $flock] $flock"
echo $Pid > $flock || die "ERROR: unable to write $flock."
setglobal wroteflock = '1'

### setup and commence tracing
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 ! echo $thresh > tracing_thresh {
	edie "ERROR: setting tracing_thresh to $thresh. Exiting."
}
if sh-expr ' opt_pid ' {
    echo '' > set_ftrace_pid
    # ftrace expects kernel pids, which are thread ids
    for tid in [/proc/$pid/task/*] {
        if ! echo $(tid##*/) >> set_ftrace_pid {
            edie "ERROR: setting -p $pid (PID exist?). Exiting."
        }
    }
}
if sh-expr ' opt_tid ' {
    if ! echo $tid > set_ftrace_pid {
        edie "ERROR: setting -L $tid (TID exist?). Exiting."
    }
}
if ! echo $funcs > set_ftrace_filter {
	edie "ERROR: enabling \"$funcs\" filter. Function exist? Exiting."
}
if ! echo $funcs > set_graph_function {
	edie "ERROR: enabling \"$funcs\" graph. Exiting."
}
if ! echo function_graph > current_tracer {
	edie "ERROR: setting current_tracer to \"function_graph\". Exiting."
}
if sh-expr ' opt_cpu ' {
	if ! echo nosleep-time > trace_options {
		edie "ERROR: setting -C (nosleep-time). Exiting."
	}
}
# the following must be done after setting current_tracer
if sh-expr ' opt_time ' {
	if ! echo funcgraph-abstime > trace_options {
		edie "ERROR: setting -t (funcgraph-abstime). Exiting."
	}
}
if sh-expr ' opt_proc ' {
	if ! echo funcgraph-proc > trace_options {
		edie "ERROR: setting -P (funcgraph-proc). Exiting."
	}
}

### setup output filter
setglobal cat = 'cat'
if sh-expr ' opt_proc ' {
	# remove proc change entries, since PID is included. example:
	#  ------------------------------------------
	#  0)  supervi-1699  =>  supervi-1693 
	#  ------------------------------------------
	#
	setglobal cat = "$awk' "/(^ ---|^$)/ || \$3 == \"=>\" { next } { print \$0 }""'
}

### print trace buffer
warn "echo > trace"
if sh-expr ' opt_duration ' {
	sleep $duration
	if sh-expr ' opt_headers ' {
		$cat trace
	} else {
		$cat trace | grep -v '^#'
	}
} else {
	# trace_pipe lack headers, so fetch them from trace
	sh-expr ' opt_headers )'&& cat trace
	eval $cat trace_pipe
}

### end tracing
end