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
20 me=$(($1 * 1000))
21 jittering=$2
22 duration=$3
23 sleepmax=${4-1000000}
24 spinmax=${5-1000}
25
26 n=1
27
28 starttime=`gawk 'BEGIN { print systime(); }' < /dev/null`
29
30 nohotplugcpus=
31 for i in /sys/devices/system/cpu/cpu[0-9]*
32 do
33 if test -f $i/online
34 then
35 :
36 else
37 curcpu=`echo $i | sed -e 's/^[^0-9]*//'`
38 nohotplugcpus="$nohotplugcpus $curcpu"
39 fi
40 done
41
42 while :
43 do
44 # Check for done.
45 t=`gawk -v s=$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
98 done
99
100 exit 1
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