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 CPU
38	cpus=`ls /sys/devices/system/cpu/*/online |
39		sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//' |
40		grep -v '^0*$'`
41	cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
42		srand(n + me + systime());
43		ncpus = split(cpus, ca);
44		curcpu = ca[int(rand() * ncpus + 1)];
45		mask = lshift(1, curcpu);
46		if (mask + 0 <= 0)
47			mask = 1;
48		printf("%#x\n", mask);
49	}' < /dev/null`
50	n=$(($n+1))
51	if ! taskset -p $cpumask $$ > /dev/null 2>&1
52	then
53		echo taskset failure: '"taskset -p ' $cpumask $$ '"'
54		exit 1
55	fi
56
57	# Sleep a random duration
58	sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
59		srand(n + me + systime());
60		printf("%06d", int(rand() * sleepmax));
61	}' < /dev/null`
62	n=$(($n+1))
63	sleep .$sleeptime
64
65	# Spin a random duration
66	limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
67		srand(n + me + systime());
68		printf("%06d", int(rand() * spinmax));
69	}' < /dev/null`
70	n=$(($n+1))
71	for i in {1..$limit}
72	do
73		echo > /dev/null
74	done
75done
76
77exit 1
78