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 jittering-path duration [ sleepmax [ spinmax ] ]
9#
10# me: Random-number-generator seed salt.
11# duration: Time to run in seconds.
12# jittering-path: Path to file whose removal will stop this script.
13# sleepmax: Maximum microseconds to sleep, defaults to one second.
14# spinmax: Maximum microseconds to spin, defaults to one millisecond.
15#
16# Copyright (C) IBM Corporation, 2016
17#
18# Authors: Paul E. McKenney <paulmck@linux.ibm.com>
19
20me=$(($1 * 1000))
21jittering=$2
22duration=$3
23sleepmax=${4-1000000}
24spinmax=${5-1000}
25
26n=1
27
28starttime=`gawk 'BEGIN { print systime(); }' < /dev/null`
29
30nohotplugcpus=
31for i in /sys/devices/system/cpu/cpu[0-9]*
32do
33	if test -f $i/online
34	then
35		:
36	else
37		curcpu=`echo $i | sed -e 's/^[^0-9]*//'`
38		nohotplugcpus="$nohotplugcpus $curcpu"
39	fi
40done
41
42while :
43do
44	# Check for done.
45	t=`gawk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
46	if test "$t" -gt "$duration"
47	then
48		exit 0;
49	fi
50
51	# Check for stop request.
52	if ! test -f "$jittering"
53	then
54		exit 1;
55	fi
56
57	# Set affinity to randomly selected online CPU
58	if cpus=`grep 1 /sys/devices/system/cpu/*/online 2>&1 |
59		 sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`
60	then
61		:
62	else
63		cpus=
64	fi
65	# Do not leave out non-hot-pluggable CPUs
66	cpus="$cpus $nohotplugcpus"
67
68	cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
69		srand(n + me + systime());
70		ncpus = split(cpus, ca);
71		print ca[int(rand() * ncpus + 1)];
72	}' < /dev/null`
73	n=$(($n+1))
74	if ! taskset -c -p $cpumask $$ > /dev/null 2>&1
75	then
76		echo taskset failure: '"taskset -c -p ' $cpumask $$ '"'
77		exit 1
78	fi
79
80	# Sleep a random duration
81	sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
82		srand(n + me + systime());
83		printf("%06d", int(rand() * sleepmax));
84	}' < /dev/null`
85	n=$(($n+1))
86	sleep .$sleeptime
87
88	# Spin a random duration
89	limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
90		srand(n + me + systime());
91		printf("%06d", int(rand() * spinmax));
92	}' < /dev/null`
93	n=$(($n+1))
94	for i in {1..$limit}
95	do
96		echo > /dev/null
97	done
98done
99
100exit 1
101