#!/bin/bash
#
# bitesize - show disk I/O size as a histogram.
#            Written using Linux perf_events (aka "perf").
#
# This can be used to characterize the distribution of block device I/O
# sizes. To study I/O in more detail, see iosnoop(8).
#
# USAGE: bitesize [-h] [-b buckets] [seconds]
#    eg,
#        ./bitesize 10
#
# Run "bitesize -h" for full usage.
#
# REQUIREMENTS: perf_events and block:block_rq_issue tracepoint, which you may
# already have on recent kernels.
#
# This uses multiple counting tracepoints with different filters, one for each
# histogram bucket. While this is summarized in-kernel, the use of multiple
# tracepoints does add addiitonal overhead, which is more evident if you add
# more buckets. In the future this functionality will be available in an
# efficient way in the kernel, and this tool can be rewritten.
#
# 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)
#
# 22-Jul-2014	Brendan Gregg	Created this.

setglobal duration = '0'
setglobal buckets = '('1 8 64 128)
setglobal secsz = '512'
trap ':' INT QUIT TERM PIPE HUP

proc usage {
	cat << """ >&2
USAGE: bitesize [-h] [-b buckets] [seconds]
                 -b buckets      # specify histogram buckets (Kbytes)
                 -h              # this usage message
   eg,
       bitesize                  # trace I/O size until Ctrl-C
       bitesize 10               # trace I/O size for 10 seconds
       bitesize -b "8 16 32"     # specify custom bucket points
"""
> !2
USAGE: bitesize [-h] [-b buckets] [seconds]
                 -b buckets      # specify histogram buckets (Kbytes)
                 -h              # this usage message
   eg,
       bitesize                  # trace I/O size until Ctrl-C
       bitesize 10               # trace I/O size for 10 seconds
       bitesize -b "8 16 32"     # specify custom bucket points
END
	exit
}

proc die {
	echo >&2 @Argv> !2 "$@"
	exit 1
}

### process options
while getopts b:h opt
{
	match $opt {
	with b	setglobal buckets = '('$OPTARG) 
	with h|?	usage 
	}
}
shift $shExpr(' $OPTIND - 1 ')
setglobal tpoint = 'block:block_rq_issue'
setglobal var = 'nr_sector'
setglobal duration = $1

### convert buckets (Kbytes) to disk sectors
setglobal i = '0'
setglobal sectors = '('${buckets[*]})
sh-expr 'max_i = ${#buckets[*]} - 1'
while sh-expr ' i <= max_i ' {
	sh-expr ' sectors[$i] = ${sectors[$i]} * 1024 / $secsz '
	# avoid negative array index errors for old version bash
	if sh-expr ' i > 0 '{
		if sh-expr ' ${sectors[$i]} <= ${sectors[$i - 1]} ' {
			die "ERROR: bucket list must increase in size."
		}
	}
	sh-expr ' i++ '
}

### build list of tracepoints and filters for each histogram bucket
setglobal max_b = $(buckets[$max_i])
setglobal max_s = $(sectors[$max_i])
setglobal tpoints = ""-e $tpoint --filter \"$var < $(sectors[0])"\""
setglobal awkarray = ''
setglobal i = '0'
while sh-expr ' i < max_i ' {
	setglobal tpoints = ""$tpoints -e $tpoint --filter \"$var >= $(sectors[$i]) && ""
	setglobal tpoints = ""$tpoints $var < $(sectors[$i + 1])"\""
	setglobal awkarray = ""$awkarray buckets[$i]=$(buckets[$i]);""
	sh-expr ' i++ '
}
setglobal awkarray = ""$awkarray buckets[$max_i]=$(buckets[$max_i]);""
setglobal tpoints = ""$tpoints -e $tpoint --filter \"$var >= $(sectors[$max_i])"\""

### prepare to run
if sh-expr ' duration ' {
	setglobal etext = ""for $duration seconds""
	setglobal cmd = ""sleep $duration""
} else {
	setglobal etext = '"until Ctrl-C'"
	setglobal cmd = '"sleep 999999'"
}
echo "Tracing block I/O size (bytes), $etext..."

### run perf
setglobal out = '"-o /dev/stdout'"	# a workaround needed in linux 3.2; not by 3.4.15
setglobal stat = $[eval perf stat $tpoints -a $out $cmd !2 > !1]
if sh-expr ' $? != 0 ' {
	echo >&2 "ERROR running perf:> !2 "ERROR running perf:"
	echo >&2 $stat> !2 "$stat"
	exit
}

### find max value for ASCII histogram
setglobal most = $[echo $stat | awk -v tpoint=$tpoint '
	$2 == tpoint { gsub(/,/, ""); if ($1 > m) { m = $1 } }
	END { print m }]

### process output
echo
echo $stat | awk -v tpoint=$tpoint -v max_i=$max_i -v most=$most '
	function star(sval, smax, swidth) {
		stars = ""
		# using int could avoid error on gawk
		if (int(smax) == 0) return ""
		for (si = 0; si < (swidth * sval / smax); si++) {
			stars = stars "#"
		}
		return stars
	}
	BEGIN {
		'"$awkarray"'
		printf("            %-15s: %-8s %s\n", "Kbytes", "I/O",
		    "Distribution")
	}
	/Performance counter stats/ { i = -1 }
	# reverse order of rule set is important
	{ ok = 0 }
	$2 == tpoint { num = $1; gsub(/,/, "", num); ok = 1 }
	ok && i >= max_i {
		printf("   %10.1f -> %-10s: %-8s |%-38s|\n",
		    buckets[i], "", num, star(num, most, 38))
		next
	}
	ok && i >= 0 && i < max_i {
		printf("   %10.1f -> %-10.1f: %-8s |%-38s|\n",
		    buckets[i], buckets[i+1] - 0.1, num,
		    star(num, most, 38))
		i++
		next
	}
	ok && i == -1 {
		printf("   %10s -> %-10.1f: %-8s |%-38s|\n", "",
		    buckets[0] - 0.1, num, star(num, most, 38))
		i++
	}
'