From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752100AbeBZWCc (ORCPT ); Mon, 26 Feb 2018 17:02:32 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57606 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751890AbeBZWCW (ORCPT ); Mon, 26 Feb 2018 17:02:22 -0500 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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 09/12] torture: Default jitter off when running rcuperf Date: Mon, 26 Feb 2018 14:02:38 -0800 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20180226220225.GA32136@linux.vnet.ibm.com> References: <20180226220225.GA32136@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18022622-0008-0000-0000-000002DB9DD5 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008601; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000254; SDB=6.00995533; UDB=6.00506035; IPR=6.00774861; MB=3.00019751; MTD=3.00000008; XFM=3.00000015; UTC=2018-02-26 22:02:19 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18022622-0009-0000-0000-00003864E993 Message-Id: <1519682561-510-9-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-02-26_07:,, 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 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1802260276 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The purpose of jitter is to expose concurrency bugs due to invalid assumptions about forward progress. There is usually little point in jitter when measuring performance. This commit therefore defaults jitter off when running rcuperf. You can override this by specifying the kvm.sh "--jitter" argument -after- the "--torture rcuperf" argument. No idea why you would want this, but if you do, that is how you do it. One example of a conccurrency bug that this jitter might expose is one in which the developer assumed that a given short region of code would be guaranteed to execute within some short time limit. Such assumptions are invalid in virtualized environments because the hupervisor can preempt the guest OS at any point, even when the guest OS thinks that it has disabled interrupts. Signed-off-by: Paul E. McKenney --- tools/testing/selftests/rcutorture/bin/kvm.sh | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/tools/testing/selftests/rcutorture/bin/kvm.sh b/tools/testing/selftests/rcutorture/bin/kvm.sh index f3c3d33150a0..56610dbbdf73 100755 --- a/tools/testing/selftests/rcutorture/bin/kvm.sh +++ b/tools/testing/selftests/rcutorture/bin/kvm.sh @@ -179,6 +179,12 @@ do checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuperf\)$' '^--' TORTURE_SUITE=$2 shift + if test "$TORTURE_SUITE" = rcuperf + then + # If you really want jitter for rcuperf, specify + # it after specifying rcuperf. (But why?) + jitter=0 + fi ;; *) echo Unknown argument $1 -- 2.5.2