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#!/bin/bash
#
# Alternate sleeping and spinning on randomly selected CPUs. The purpose
# of this script is to inflict random OS jitter on a concurrently running
# test.
#
# Usage: jitter.sh me duration [ sleepmax [ spinmax ] ]
#
# me: Random-number-generator seed salt.
# duration: Time to run in seconds.
# sleepmax: Maximum microseconds to sleep, defaults to one second.
# spinmax: Maximum microseconds to spin, defaults to one millisecond.
#
# 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, you can access it online at
# http://www.gnu.org/licenses/gpl-2.0.html.
#
# Copyright (C) IBM Corporation, 2016
#
# Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
me=$(($1 * 1000))
duration=$2
sleepmax=${3-1000000}
spinmax=${4-1000}
n=1
starttime=`awk 'BEGIN { print systime(); }' < /dev/null`
while :
do
# Check for done.
t=`awk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
if test "$t" -gt "$duration"
then
exit 0;
fi
# Set affinity to randomly selected CPU
cpus=`ls /sys/devices/system/cpu/*/online |
sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//' |
grep -v '^0*$'`
cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
srand(n + me + systime());
ncpus = split(cpus, ca);
curcpu = ca[int(rand() * ncpus + 1)];
mask = lshift(1, curcpu);
if (mask + 0 <= 0)
mask = 1;
printf("%#x\n", mask);
}' < /dev/null`
n=$(($n+1))
if ! taskset -p $cpumask $$ > /dev/null 2>&1
then
echo taskset failure: '"taskset -p ' $cpumask $$ '"'
exit 1
fi
# Sleep a random duration
sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
srand(n + me + systime());
printf("%06d", int(rand() * sleepmax));
}' < /dev/null`
n=$(($n+1))
sleep .$sleeptime
# Spin a random duration
limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
srand(n + me + systime());
printf("%06d", int(rand() * spinmax));
}' < /dev/null`
n=$(($n+1))
for i in {1..$limit}
do
echo > /dev/null
done
done
exit 1
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