jitter.sh

  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 $curcpu"
 39	fi
 40done
 41
 42# Uses global variables startsecs, startns, endsecs, endns, and limit.
 43# Exit code is success for time not yet elapsed and failure otherwise.
 44function timecheck {
 45	local done=`awk -v limit=$limit \
 46			-v startsecs=$startsecs \
 47			-v startns=$startns \
 48			-v endsecs=$endsecs \
 49			-v endns=$endns < /dev/null '
 50		BEGIN {
 51			delta = (endsecs - startsecs) * 1000 * 1000;
 52			delta += int((endns - startns) / 1000);
 53			print delta >= limit;
 54		}'`
 55	return $done
 56}
 57
 58while :
 59do
 60	# Check for done.
 61	t=`gawk -v s=$starttime 'BEGIN { print systime() - s; }' < /dev/null`
 62	if test "$t" -gt "$duration"
 63	then
 64		exit 0;
 65	fi
 66
 67	# Check for stop request.
 68	if ! test -f "$jittering"
 69	then
 70		exit 1;
 71	fi
 72
 73	# Set affinity to randomly selected online CPU
 74	if cpus=`grep 1 /sys/devices/system/cpu/*/online 2>&1 |
 75		 sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//'`
 76	then
 77		:
 78	else
 79		cpus=
 80	fi
 81	# Do not leave out non-hot-pluggable CPUs
 82	cpus="$cpus $nohotplugcpus"
 83
 84	cpumask=`awk -v cpus="$cpus" -v me=$me -v n=$n 'BEGIN {
 85		srand(n + me + systime());
 86		ncpus = split(cpus, ca);
 87		print ca[int(rand() * ncpus + 1)];
 88	}' < /dev/null`
 89	n=$(($n+1))
 90	if ! taskset -c -p $cpumask $$ > /dev/null 2>&1
 91	then
 92		echo taskset failure: '"taskset -c -p ' $cpumask $$ '"'
 93		exit 1
 94	fi
 95
 96	# Sleep a random duration
 97	sleeptime=`awk -v me=$me -v n=$n -v sleepmax=$sleepmax 'BEGIN {
 98		srand(n + me + systime());
 99		printf("%06d", int(rand() * sleepmax));
100	}' < /dev/null`
101	n=$(($n+1))
102	sleep .$sleeptime
103
104	# Spin a random duration, but with rather coarse granularity.
105	limit=`awk -v me=$me -v n=$n -v spinmax=$spinmax 'BEGIN {
106		srand(n + me + systime());
107		printf("%06d", int(rand() * spinmax));
108	}' < /dev/null`
109	n=$(($n+1))
110	startsecs=`date +%s`
111	startns=`date +%N`
112	endsecs=$startns
113	endns=$endns
114	while timecheck
115	do
116		endsecs=`date +%s`
117		endns=`date +%N`
118	done
119done
120
121exit 1