From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751997AbdJDVVu (ORCPT ); Wed, 4 Oct 2017 17:21:50 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43602 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751868AbdJDVVc (ORCPT ); Wed, 4 Oct 2017 17:21:32 -0400 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 03/16] documentation: Slow systems can stall RCU grace periods Date: Wed, 4 Oct 2017 14:21:13 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20171004212051.GA8411@linux.vnet.ibm.com> References: <20171004212051.GA8411@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17100421-0056-0000-0000-000003D3C73B X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007843; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000233; SDB=6.00926530; UDB=6.00466099; IPR=6.00706743; BA=6.00005620; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017394; XFM=3.00000015; UTC=2017-10-04 21:21:30 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17100421-0057-0000-0000-0000080AD711 Message-Id: <1507152086-9791-3-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-04_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710040296 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If a fast system has a worst-case grace-period duration of (say) ten seconds, then running the same workload on a system ten times as slow will get you an RCU CPU stall warning given default stall-warning timeout settings. This commit therefore adds this possibility to stallwarn.txt. Reported-by: Daniel Lezcano Signed-off-by: Paul E. McKenney --- Documentation/RCU/stallwarn.txt | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index 21b8913acbdf..238acbd94917 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -70,6 +70,12 @@ o A periodic interrupt whose handler takes longer than the time considerably longer than normal, which can in turn result in RCU CPU stall warnings. +o Testing a workload on a fast system, tuning the stall-warning + timeout down to just barely avoid RCU CPU stall warnings, and then + running the same workload with the same stall-warning timeout on a + slow system. Note that thermal throttling and on-demand governors + can cause a single system to be sometimes fast and sometimes slow! + o A hardware or software issue shuts off the scheduler-clock interrupt on a CPU that is not in dyntick-idle mode. This problem really has happened, and seems to be most likely to -- 2.5.2