1#!/bin/bash
2# SPDX-License-Identifier: GPL-2.0+
3#
4# Alternate sleeping and spinning on randomly selected CPUs.  The purpose
5# of this script is to inflict random OS jitter on a concurrently running
6# test.
7#
8# Usage: jitter.sh me duration [ sleepmax [ spinmax ] ]
9#
10# me: Random-number-generator seed salt.
11# duration: Time to run in seconds.
12# sleepmax: Maximum microseconds to sleep, defaults to one second.
13# spinmax: Maximum microseconds to spin, defaults to one millisecond.
14#
15# Copyright (C) IBM Corporation, 2016
16#
17# Authors: Paul E. McKenney <paulmck@linux.ibm.com>
18
19me=$(($1 * 1000))
20duration=$2
21sleepmax=${3-1000000}
22spinmax=${4-1000}
23
24n=1
25
26starttime=`awk 'BEGIN { print systime(); }' < /dev/null`
27
28while :
29do
30	# Check for done.
31	t=`awk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
32	if test "$t" -gt "$duration"
33	then
34		exit 0;
35	fi
36
37	# Set affinity to randomly selected online CPU
38	cpus=`grep 1 /sys/devices/system/cpu/*/online |
39		sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`
40
41	# Do not leave out poor old cpu0 which may not be hot-pluggable
42	if [ ! -f "/sys/devices/system/cpu/cpu0/online" ]; then
43		cpus="0 $cpus"
44	fi
45
46	cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
47		srand(n + me + systime());
48		ncpus = split(cpus, ca);
49		curcpu = ca[int(rand() * ncpus + 1)];
50		mask = lshift(1, curcpu);
51		if (mask + 0 <= 0)
52			mask = 1;
53		printf("%#x\n", mask);
54	}' < /dev/null`
55	n=$(($n+1))
56	if ! taskset -p $cpumask $$ > /dev/null 2>&1
57	then
58		echo taskset failure: '"taskset -p ' $cpumask $$ '"'
59		exit 1
60	fi
61
62	# Sleep a random duration
63	sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
64		srand(n + me + systime());
65		printf("%06d", int(rand() * sleepmax));
66	}' < /dev/null`
67	n=$(($n+1))
68	sleep .$sleeptime
69
70	# Spin a random duration
71	limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
72		srand(n + me + systime());
73		printf("%06d", int(rand() * spinmax));
74	}' < /dev/null`
75	n=$(($n+1))
76	for i in {1..$limit}
77	do
78		echo > /dev/null
79	done
80done
81
82exit 1
83