#!/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 $interval (( opt_timestamp )) && printf "%(%H:%M:%S)T " -1 # cat both meminfo and trace stats, and let awk pick them apart cat /proc/meminfo trace_stat/function* | awk -v debug=$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"