101 lines · bash
1#!/bin/bash2# SPDX-License-Identifier: GPL-2.0+3#4# Alternate sleeping and spinning on randomly selected CPUs. The purpose5# of this script is to inflict random OS jitter on a concurrently running6# test.7#8# Usage: jitter.sh me jittering-path duration [ sleepmax [ spinmax ] ]9#10# me: Random-number-generator seed salt.11# duration: Time to run in seconds.12# jittering-path: Path to file whose removal will stop this script.13# sleepmax: Maximum microseconds to sleep, defaults to one second.14# spinmax: Maximum microseconds to spin, defaults to one millisecond.15#16# Copyright (C) IBM Corporation, 201617#18# Authors: Paul E. McKenney <paulmck@linux.ibm.com>19 20me=$(($1 * 1000))21jittering=$222duration=$323sleepmax=${4-1000000}24spinmax=${5-1000}25 26n=127 28starttime=`gawk 'BEGIN { print systime(); }' < /dev/null`29 30nohotplugcpus=31for i in /sys/devices/system/cpu/cpu[0-9]*32do33 if test -f $i/online34 then35 :36 else37 curcpu=`echo $i | sed -e 's/^[^0-9]*//'`38 nohotplugcpus="$nohotplugcpus $curcpu"39 fi40done41 42while :43do44 # Check for done.45 t=`gawk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`46 if test "$t" -gt "$duration"47 then48 exit 0;49 fi50 51 # Check for stop request.52 if ! test -f "$jittering"53 then54 exit 1;55 fi56 57 # Set affinity to randomly selected online CPU58 if cpus=`grep 1 /sys/devices/system/cpu/*/online 2>&1 |59 sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`60 then61 :62 else63 cpus=64 fi65 # Do not leave out non-hot-pluggable CPUs66 cpus="$cpus $nohotplugcpus"67 68 cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {69 srand(n + me + systime());70 ncpus = split(cpus, ca);71 print ca[int(rand() * ncpus + 1)];72 }' < /dev/null`73 n=$(($n+1))74 if ! taskset -c -p $cpumask $$ > /dev/null 2>&175 then76 echo taskset failure: '"taskset -c -p ' $cpumask $$ '"'77 exit 178 fi79 80 # Sleep a random duration81 sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {82 srand(n + me + systime());83 printf("%06d", int(rand() * sleepmax));84 }' < /dev/null`85 n=$(($n+1))86 sleep .$sleeptime87 88 # Spin a random duration89 limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {90 srand(n + me + systime());91 printf("%06d", int(rand() * spinmax));92 }' < /dev/null`93 n=$(($n+1))94 for i in {1..$limit}95 do96 echo > /dev/null97 done98done99 100exit 1101