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#!/bin/bash | |
# | |
# cachestat - show Linux page cache hit/miss statistics. | |
# Uses Linux ftrace. | |
# | |
# This is a proof of concept using Linux ftrace capabilities on older kernels, | |
# and works by using function profiling for in-kernel counters. Specifically, | |
# four kernel functions are traced: | |
# | |
# mark_page_accessed() for measuring cache accesses | |
# mark_buffer_dirty() for measuring cache writes | |
# add_to_page_cache_lru() for measuring page additions | |
# account_page_dirtied() for measuring page dirties | |
# | |
# It is possible that these functions have been renamed (or are different | |
# logically) for your kernel version, and this script will not work as-is. | |
# This script was written on Linux 3.13. This script is a sandcastle: the | |
# kernel may wash some away, and you'll need to rebuild. | |
# | |
# USAGE: cachestat [-Dht] [interval] | |
# eg, | |
# cachestat 5 # show stats every 5 seconds | |
# | |
# Run "cachestat -h" for full usage. | |
# | |
# WARNING: This uses dynamic tracing of kernel functions, and could cause | |
# kernel panics or freezes. Test, and know what you are doing, before use. | |
# It also traces cache activity, which can be frequent, and cost some overhead. | |
# The statistics should be treated as best-effort: there may be some error | |
# margin depending on unusual workload types. | |
# | |
# REQUIREMENTS: CONFIG_FUNCTION_PROFILER, awk. | |
# | |
# 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) | |
# | |
# 28-Dec-2014 Brendan Gregg Created this. | |
### default variables | |
tracing=/sys/kernel/debug/tracing | |
interval=1; opt_timestamp=0; opt_debug=0 | |
trap 'quit=1' INT QUIT TERM PIPE HUP # sends execution to end tracing section | |
function usage { | |
cat <<-END >&2 | |
USAGE: cachestat [-Dht] [interval] | |
-D # print debug counters | |
-h # this usage message | |
-t # include timestamp | |
interval # output interval in secs (default 1) | |
eg, | |
cachestat # show stats every second | |
cachestat 5 # show stats every 5 seconds | |
See the man page and example file for more info. | |
END | |
exit | |
} | |
function warn { | |
if ! eval "$@"; then | |
echo >&2 "WARNING: command failed \"$@\"" | |
fi | |
} | |
function die { | |
echo >&2 "$@" | |
exit 1 | |
} | |
### process options | |
while getopts Dht opt | |
do | |
case $opt in | |
D) opt_debug=1 ;; | |
t) opt_timestamp=1 ;; | |
h|?) usage ;; | |
esac | |
done | |
shift $(( $OPTIND - 1 )) | |
### option logic | |
if (( $# )); then | |
interval=$1 | |
fi | |
echo "Counting cache functions... Output every $interval seconds." | |
### check permissions | |
cd $tracing || die "ERROR: accessing tracing. Root user? Kernel has FTRACE? | |
debugfs mounted? (mount -t debugfs debugfs /sys/kernel/debug)" | |
### enable tracing | |
sysctl -q kernel.ftrace_enabled=1 # doesn't set exit status | |
printf "mark_page_accessed\nmark_buffer_dirty\nadd_to_page_cache_lru\naccount_page_dirtied\n" > set_ftrace_filter || \ | |
die "ERROR: tracing these four kernel functions: mark_page_accessed,"\ | |
"mark_buffer_dirty, add_to_page_cache_lru and account_page_dirtied (unknown kernel version?). Exiting." | |
warn "echo nop > current_tracer" | |
if ! echo 1 > function_profile_enabled; then | |
echo > set_ftrace_filter | |
die "ERROR: enabling function profiling. Have CONFIG_FUNCTION_PROFILER? Exiting." | |
fi | |
(( opt_timestamp )) && printf "%-8s " TIME | |
printf "%8s %8s %8s %8s %12s %10s" HITS MISSES DIRTIES RATIO "BUFFERS_MB" "CACHE_MB" | |
(( opt_debug )) && printf " DEBUG" | |
echo | |
### summarize | |
quit=0; secs=0 | |
while (( !quit && (!opt_duration || secs < duration) )); do | |
(( secs += interval )) | |
echo 0 > function_profile_enabled | |
echo 1 > function_profile_enabled | |
sleep $interval | |
# fix printf %(FORMAT)T on centos6 | |
(( opt_timestamp )) && (printf "%(%H:%M:%S)T " -1 2>/dev/null || printf "%8s " $(date '+%H:%M:%S')) | |
# cat both meminfo and trace stats, and let awk pick them apart | |
cat /proc/meminfo trace_stat/function* | awk -v debug=$opt_debug ' | |
# match meminfo stats: | |
$1 == "Buffers:" && $3 == "kB" { buffers_mb = $2 / 1024 } | |
$1 == "Cached:" && $3 == "kB" { cached_mb = $2 / 1024 } | |
# identify and save trace counts: | |
$2 ~ /[0-9]/ && $3 != "kB" { a[$1] += $2 } | |
END { | |
mpa = a["mark_page_accessed"] | |
mbd = a["mark_buffer_dirty"] | |
apcl = a["add_to_page_cache_lru"] | |
apd = a["account_page_dirtied"] | |
total = mpa - mbd | |
misses = apcl - apd | |
if (misses < 0) | |
misses = 0 | |
hits = total - misses | |
ratio = 100 * hits / total | |
printf "%8d %8d %8d %7.1f%% %12.0f %10.0f", hits, misses, mbd, | |
ratio, buffers_mb, cached_mb | |
if (debug) | |
printf " (%d %d %d %d)", mpa, mbd, apcl, apd | |
printf "\n" | |
}' | |
done | |
### end tracing | |
echo 2>/dev/null | |
echo "Ending tracing..." 2>/dev/null | |
warn "echo 0 > function_profile_enabled" | |
warn "echo > set_ftrace_filter" |
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