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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 9 Jan 2019 21:50:11 -0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x09LoAsL24707180 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 9 Jan 2019 21:50:10 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7582DB206B; Wed, 9 Jan 2019 21:50:10 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 550B9B2068; Wed, 9 Jan 2019 21:50:10 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.88]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 9 Jan 2019 21:50:10 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 2AB5216C63C9; Wed, 9 Jan 2019 13:50:10 -0800 (PST) From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 02/10] torture: Explain and simplify odd "for" loop in mkinitrd.sh Date: Wed, 9 Jan 2019 13:50:00 -0800 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190109214944.GA5610@linux.ibm.com> References: <20190109214944.GA5610@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19010921-0052-0000-0000-00000375B6C1 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010375; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000274; SDB=6.01144152; UDB=6.00595713; IPR=6.00924414; MB=3.00025056; MTD=3.00000008; XFM=3.00000015; UTC=2019-01-09 21:50:15 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19010921-0053-0000-0000-00005F67A01E Message-Id: <20190109215008.6401-2-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-09_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901090173 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Why a Bourne-shell "for" loop? And why 192 instances of "a"? This commit adds a shell comment to present the answer to these mysteries. It also uses a series of factor-of-four Bourne-shell assignments to make it easy to see how many instances there are, replacing the earlier wall of 'a' characters. Reported-by: Josh Triplett Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett [ paulmck: Fix wrong-variable bugs noted by Andrea Parri. ] --- .../selftests/rcutorture/bin/mkinitrd.sh | 23 ++++++++++++------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh index da298394daa2..e79eb35c41e2 100755 --- a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh +++ b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh @@ -40,17 +40,24 @@ mkdir $T cat > $T/init << '__EOF___' #!/bin/sh # Run in userspace a few milliseconds every second. This helps to -# exercise the NO_HZ_FULL portions of RCU. +# exercise the NO_HZ_FULL portions of RCU. The 192 instances of "a" was +# empirically shown to give a nice multi-millisecond burst of user-mode +# execution on a 2GHz CPU, as desired. Modern CPUs will vary from a +# couple of milliseconds up to perhaps 100 milliseconds, which is an +# acceptable range. +# +# Why not calibrate an exact delay? Because within this initrd, we +# are restricted to Bourne-shell builtins, which as far as I know do not +# provide any means of obtaining a fine-grained timestamp. + +a4="a a a a" +a16="$a4 $a4 $a4 $a4" +a64="$a16 $a16 $a16 $a16" +a192="$a64 $a64 $a64" while : do q= - for i in \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a + for i in $a192 do q="$q $i" done -- 2.17.1