#!/bin/bash
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#
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# Alternate sleeping and spinning on randomly selected CPUs. The purpose
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# of this script is to inflict random OS jitter on a concurrently running
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# test.
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#
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# Usage: jitter.sh me duration [ sleepmax [ spinmax ] ]
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#
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# me: Random-number-generator seed salt.
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# duration: Time to run in seconds.
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# sleepmax: Maximum microseconds to sleep, defaults to one second.
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# spinmax: Maximum microseconds to spin, defaults to one millisecond.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, you can access it online at
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# http://www.gnu.org/licenses/gpl-2.0.html.
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#
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# Copyright (C) IBM Corporation, 2016
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#
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# Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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me=$(($1 * 1000))
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duration=$2
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sleepmax=${3-1000000}
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spinmax=${4-1000}
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n=1
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starttime=`awk 'BEGIN { print systime(); }' < /dev/null`
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while :
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do
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# Check for done.
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t=`awk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
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if test "$t" -gt "$duration"
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then
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exit 0;
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fi
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# Set affinity to randomly selected CPU
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cpus=`ls /sys/devices/system/cpu/*/online |
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sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//' |
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grep -v '^0*$'`
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cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
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srand(n + me + systime());
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ncpus = split(cpus, ca);
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curcpu = ca[int(rand() * ncpus + 1)];
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mask = lshift(1, curcpu);
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if (mask + 0 <= 0)
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mask = 1;
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printf("%#x\n", mask);
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}' < /dev/null`
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n=$(($n+1))
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if ! taskset -p $cpumask $$ > /dev/null 2>&1
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then
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echo taskset failure: '"taskset -p ' $cpumask $$ '"'
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exit 1
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fi
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# Sleep a random duration
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sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
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srand(n + me + systime());
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printf("%06d", int(rand() * sleepmax));
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}' < /dev/null`
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n=$(($n+1))
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sleep .$sleeptime
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# Spin a random duration
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limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
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srand(n + me + systime());
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printf("%06d", int(rand() * spinmax));
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}' < /dev/null`
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n=$(($n+1))
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for i in {1..$limit}
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do
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echo > /dev/null
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done
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done
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exit 1
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