#!/bin/bash # # iolatency - summarize block device I/O latency as a histogram. # Written using Linux ftrace. # # This shows the distribution of latency, allowing modes and latency outliers # to be identified and studied. # # USAGE: ./iolatency [-hQT] [-d device] [-i iotype] [interval [count]] # # REQUIREMENTS: FTRACE CONFIG and block:block_rq_* tracepoints, which you may # already have on recent kernels. # # OVERHEAD: block device I/O issue and completion events are traced and buffered # in-kernel, then processed and summarized in user space. There may be # measurable overhead with this approach, relative to the block device IOPS. # # This was written as a proof of concept for ftrace. # # 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) # # 20-Jul-2014 Brendan Gregg Created this. ### default variables tracing=/sys/kernel/debug/tracing flock=/var/tmp/.ftrace-lock bufsize_kb=4096 opt_device=0; device=; opt_iotype=0; iotype=; opt_timestamp=0 opt_interval=0; interval=1; opt_count=0; count=0; opt_queue=0 trap ':' INT QUIT TERM PIPE HUP # sends execution to end tracing section function usage { cat <<-END >&2 USAGE: iolatency [-hQT] [-d device] [-i iotype] [interval [count]] -d device # device string (eg, "202,1) -i iotype # match type (eg, '*R*' for all reads) -Q # use queue insert as start time -T # timestamp on output -h # this usage message interval # summary interval, seconds (default 1) count # number of summaries eg, iolatency # summarize latency every second iolatency -Q # include block I/O queue time iolatency 5 2 # 2 x 5 second summaries iolatency -i '*R*' # trace reads iolatency -d 202,1 # trace device 202,1 only See the man page and example file for more info. END exit } function warn { if ! eval "$@"; then echo >&2 "WARNING: command failed \"$@\"" fi } function end { # disable tracing echo 2>/dev/null echo "Ending tracing..." 2>/dev/null cd $tracing warn "echo 0 > events/block/$b_start/enable" warn "echo 0 > events/block/block_rq_complete/enable" if (( opt_device || opt_iotype )); then warn "echo 0 > events/block/$b_start/filter" warn "echo 0 > events/block/block_rq_complete/filter" fi warn "echo > trace" (( wroteflock )) && warn "rm $flock" } function die { echo >&2 "$@" exit 1 } function edie { # die with a quiet end() echo >&2 "$@" exec >/dev/null 2>&1 end exit 1 } ### process options while getopts d:hi:QT opt do case $opt in d) opt_device=1; device=$OPTARG ;; i) opt_iotype=1; iotype=$OPTARG ;; Q) opt_queue=1 ;; T) opt_timestamp=1 ;; h|?) usage ;; esac done shift $(( $OPTIND - 1 )) if (( $# )); then opt_interval=1 interval=$1 shift fi if (( $# )); then opt_count=1 count=$1 fi if (( opt_device )); then major=${device%,*} minor=${device#*,} dev=$(( (major << 20) + minor )) fi if (( opt_queue )); then b_start=block_rq_insert else b_start=block_rq_issue fi ### select awk [[ -x /usr/bin/mawk ]] && awk='mawk -W interactive' || 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 $$ > $flock || die "ERROR: unable to write $flock." wroteflock=1 ### setup and begin tracing warn "echo nop > current_tracer" warn "echo $bufsize_kb > buffer_size_kb" filter= if (( opt_iotype )); then filter="rwbs ~ \"$iotype\"" fi if (( opt_device )); then [[ "$filter" != "" ]] && filter="$filter && " filter="${filter}dev == $dev" fi if (( opt_iotype || opt_device )); then if ! echo "$filter" > events/block/$b_start/filter || \ ! echo "$filter" > events/block/block_rq_complete/filter then edie "ERROR: setting -d or -t filter. Exiting." fi fi if ! echo 1 > events/block/$b_start/enable || \ ! echo 1 > events/block/block_rq_complete/enable; then edie "ERROR: enabling block I/O tracepoints. Exiting." fi etext= (( !opt_count )) && etext=" Ctrl-C to end." echo "Tracing block I/O. Output every $interval seconds.$etext" # # Determine output format. It may be one of the following (newest first): # TASK-PID CPU# |||| TIMESTAMP FUNCTION # TASK-PID CPU# TIMESTAMP FUNCTION # To differentiate between them, the number of header fields is counted, # and an offset set, to skip the extra column when needed. # offset=$($awk 'BEGIN { o = 0; } $1 == "#" && $2 ~ /TASK/ && NF == 6 { o = 1; } $2 ~ /TASK/ { print o; exit }' trace) ### print trace buffer warn "echo > trace" i=0 while (( !opt_count || (i < count) )); do (( i++ )) sleep $interval # snapshots were added in 3.10 if [[ -x snapshot ]]; then echo 1 > snapshot echo > trace cat snapshot else cat trace echo > trace fi (( opt_timestamp )) && printf "time %(%H:%M:%S)T:\n" -1 echo "tick" done | \ $awk -v o=$offset -v opt_timestamp=$opt_timestamp -v b_start=$b_start ' function star(sval, smax, swidth) { stars = "" if (smax == 0) return "" for (si = 0; si < (swidth * sval / smax); si++) { stars = stars "#" } return stars } BEGIN { max_i = 0 } # common fields $1 != "#" { time = $(3+o); sub(":", "", time) dev = $(5+o) } # block I/O request $1 != "#" && $0 ~ b_start { # # example: (fields1..4+o) 202,1 W 0 () 12862264 + 8 [tar] # The cmd field "()" might contain multiple words (hex), # hence stepping from the right (NF-3). # loc = $(NF-3) starts[dev, loc] = time next } # block I/O completion $1 != "#" && $0 ~ /rq_complete/ { # # example: (fields1..4+o) 202,1 W () 12862256 + 8 [0] # dir = $(6+o) loc = $(NF-3) if (starts[dev, loc] > 0) { latency_ms = 1000 * (time - starts[dev, loc]) i = 0 for (ms = 1; latency_ms > ms; ms *= 2) { i++ } hist[i]++ if (i > max_i) max_i = i delete starts[dev, loc] } next } # timestamp $1 == "time" { lasttime = $2 } # print summary $1 == "tick" { print "" if (opt_timestamp) print lasttime # find max value max_v = 0 for (i = 0; i <= max_i; i++) { if (hist[i] > max_v) max_v = hist[i] } # print histogram printf "%8s .. %-8s: %-8s |%-38s|\n", ">=(ms)", "<(ms)", "I/O", "Distribution" ms = 1 from = 0 for (i = 0; i <= max_i; i++) { printf "%8d -> %-8d: %-8d |%-38s|\n", from, ms, hist[i], star(hist[i], max_v, 38) from = ms ms *= 2 } fflush() delete hist delete starts # invalid if events missed between snapshots max_i = 0 } $0 ~ /LOST.*EVENTS/ { print "WARNING: " $0 > "/dev/stderr" } ' ### end tracing end