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#!/bin/bash
# SPDX-License-Identifier: GPL-2.0+
#
# 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 jittering-path duration [ sleepmax [ spinmax ] ]
#
# me: Random-number-generator seed salt.
# duration: Time to run in seconds.
# jittering-path: Path to file whose removal will stop this script.
# sleepmax: Maximum microseconds to sleep, defaults to one second.
# spinmax: Maximum microseconds to spin, defaults to one millisecond.
#
# Copyright (C) IBM Corporation, 2016
#
# Authors: Paul E. McKenney <paulmck@linux.ibm.com>
me=$(($1 * 1000))
jittering=$2
duration=$3
sleepmax=${4-1000000}
spinmax=${5-1000}
n=1
starttime=`gawk 'BEGIN { print systime(); }' < /dev/null`
nohotplugcpus=
for i in /sys/devices/system/cpu/cpu[0-9]*
do
if test -f $i/online
then
:
else
curcpu=`echo $i | sed -e 's/^[^0-9]*//'`
nohotplugcpus="$nohotplugcpus $curcpu"
fi
done
while :
do
# Check for done.
t=`gawk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
if test "$t" -gt "$duration"
then
exit 0;
fi
# Check for stop request.
if ! test -f "$jittering"
then
exit 1;
fi
# Set affinity to randomly selected online CPU
if cpus=`grep 1 /sys/devices/system/cpu/*/online 2>&1 |
sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`
then
:
else
cpus=
fi
# Do not leave out non-hot-pluggable CPUs
cpus="$cpus $nohotplugcpus"
cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
srand(n + me + systime());
ncpus = split(cpus, ca);
print ca[int(rand() * ncpus + 1)];
}' < /dev/null`
n=$(($n+1))
if ! taskset -c -p $cpumask $$ > /dev/null 2>&1
then
echo taskset failure: '"taskset -c -p ' $cpumask $$ '"'
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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