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	# Check for stop request.
50	if test -f "$TORTURE_STOPFILE"
51	then
52		exit 1;
53	fi
54
55	# Set affinity to randomly selected online CPU
56	if cpus=`grep 1 /sys/devices/system/cpu/*/online 2>&1 |
57		 sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`
58	then
59		:
60	else
61		cpus=
62	fi
63	# Do not leave out non-hot-pluggable CPUs
64	cpus="$cpus $nohotplugcpus"
65
66	cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
67		srand(n + me + systime());
68		ncpus = split(cpus, ca);
69		curcpu = ca[int(rand() * ncpus + 1)];
70		mask = lshift(1, curcpu);
71		if (mask + 0 <= 0)
72			mask = 1;
73		printf("%#x\n", mask);
74	}' < /dev/null`
75	n=$(($n+1))
76	if ! taskset -p $cpumask $$ > /dev/null 2>&1
77	then
78		echo taskset failure: '"taskset -p ' $cpumask $$ '"'
79		exit 1
80	fi
81
82	# Sleep a random duration
83	sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
84		srand(n + me + systime());
85		printf("%06d", int(rand() * sleepmax));
86	}' < /dev/null`
87	n=$(($n+1))
88	sleep .$sleeptime
89
90	# Spin a random duration
91	limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
92		srand(n + me + systime());
93		printf("%06d", int(rand() * spinmax));
94	}' < /dev/null`
95	n=$(($n+1))
96	for i in {1..$limit}
97	do
98		echo > /dev/null
99	done
100done
101
102exit 1
103