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=`gawk 'BEGIN { print systime(); }' < /dev/null`
27
28nohotplugcpus=
29for i in /sys/devices/system/cpu/cpu[0-9]*
30do
31	if test -f $i/online
32	then
33		:
34	else
35		curcpu=`echo $i | sed -e 's/^[^0-9]*//'`
36		nohotplugcpus="$nohotplugcpus $curcpu"
37	fi
38done
39
40while :
41do
42	# Check for done.
43	t=`gawk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
44	if test "$t" -gt "$duration"
45	then
46		exit 0;
47	fi
48
49	# Set affinity to randomly selected online CPU
50	if cpus=`grep 1 /sys/devices/system/cpu/*/online 2>&1 |
51		 sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`
52	then
53		:
54	else
55		cpus=
56	fi
57	# Do not leave out non-hot-pluggable CPUs
58	cpus="$cpus $nohotplugcpus"
59
60	cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
61		srand(n + me + systime());
62		ncpus = split(cpus, ca);
63		curcpu = ca[int(rand() * ncpus + 1)];
64		mask = lshift(1, curcpu);
65		if (mask + 0 <= 0)
66			mask = 1;
67		printf("%#x\n", mask);
68	}' < /dev/null`
69	n=$(($n+1))
70	if ! taskset -p $cpumask $$ > /dev/null 2>&1
71	then
72		echo taskset failure: '"taskset -p ' $cpumask $$ '"'
73		exit 1
74	fi
75
76	# Sleep a random duration
77	sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
78		srand(n + me + systime());
79		printf("%06d", int(rand() * sleepmax));
80	}' < /dev/null`
81	n=$(($n+1))
82	sleep .$sleeptime
83
84	# Spin a random duration
85	limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
86		srand(n + me + systime());
87		printf("%06d", int(rand() * spinmax));
88	}' < /dev/null`
89	n=$(($n+1))
90	for i in {1..$limit}
91	do
92		echo > /dev/null
93	done
94done
95
96exit 1
97