2 # SPDX-License-Identifier: GPL-2.0+
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
8 # Usage: jitter.sh me jittering-path duration [ sleepmax [ spinmax ] ]
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.
16 # Copyright (C) IBM Corporation, 2016
18 # Authors: Paul E. McKenney <paulmck@linux.ibm.com>
28 starttime=`gawk 'BEGIN { print systime(); }' < /dev/null`
31 for i in /sys/devices/system/cpu/cpu[0-9]*
37 curcpu=`echo $i | sed -e 's/^[^0-9]*//'`
38 nohotplugcpus="$nohotplugcpus $curcpu"
45 t=`gawk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
46 if test "$t" -gt "$duration"
51 # Check for stop request.
52 if ! test -f "$jittering"
57 # Set affinity to randomly selected online CPU
58 if cpus=`grep 1 /sys/devices/system/cpu/*/online 2>&1 |
59 sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`
65 # Do not leave out non-hot-pluggable CPUs
66 cpus="$cpus $nohotplugcpus"
68 cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
69 srand(n + me + systime());
70 ncpus = split(cpus, ca);
71 curcpu = ca[int(rand() * ncpus + 1)];
73 for (i = 1; 4 * i <= curcpu; i++)
75 print "0x" 2 ^ (curcpu % 4) z;
78 if ! taskset -p $cpumask $$ > /dev/null 2>&1
80 echo taskset failure: '"taskset -p ' $cpumask $$ '"'
84 # Sleep a random duration
85 sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
86 srand(n + me + systime());
87 printf("%06d", int(rand() * sleepmax));
92 # Spin a random duration
93 limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
94 srand(n + me + systime());
95 printf("%06d", int(rand() * spinmax));