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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 18 Jun 2018 22:37:00 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w5J2axHk16318744 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 19 Jun 2018 02:36:59 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 95212B2067; Mon, 18 Jun 2018 22:36:49 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 73076B2064; Mon, 18 Jun 2018 22:36:49 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.187.236]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 18 Jun 2018 22:36:49 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 4FA5A16C2AF0; Mon, 18 Jun 2018 19:38:59 -0700 (PDT) Date: Mon, 18 Jun 2018 19:38:59 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: Joel Fernandes , kernel test robot , linux-kernel@vger.kernel.org, kernel-team@android.com, Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , mingo@redhat.com, Steven Rostedt , tglx@linutronix.de, lkp@01.org Subject: Re: [lkp-robot] [rcutorture] 46e26223e3: WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print Reply-To: paulmck@linux.vnet.ibm.com References: <20180610234544.150933-2-joel@joelfernandes.org> <20180613065711.GZ16472@yexl-desktop> <20180613072948.GA142000@joelaf.mtv.corp.google.com> <20180618165646.GA3593@linux.vnet.ibm.com> <20180618222647.GA156172@joelaf.mtv.corp.google.com> <20180619010803.GC3593@linux.vnet.ibm.com> <2CDE3A5B-1AD3-4185-9E24-24D4075A9EA6@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2CDE3A5B-1AD3-4185-9E24-24D4075A9EA6@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18061902-0064-0000-0000-0000031D2233 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009217; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000265; SDB=6.01049034; UDB=6.00537486; IPR=6.00828007; MB=3.00021729; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-19 02:37:03 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18061902-0065-0000-0000-000039A402D0 Message-Id: <20180619023859.GE3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-19_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 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=8.0.1-1805220000 definitions=main-1806190028 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 18, 2018 at 06:36:06PM -0700, Joel Fernandes wrote: > > > On June 18, 2018 6:08:03 PM PDT, "Paul E. McKenney" wrote: > >On Mon, Jun 18, 2018 at 03:26:47PM -0700, Joel Fernandes wrote: > >> On Mon, Jun 18, 2018 at 09:56:46AM -0700, Paul E. McKenney wrote: > >> > > The reason for the rcutorture test failure could be that the > >default > >> > > kthread_prio for the system's RCU threads is set to 1 (unless > >overridden by > >> > > rcutree.kthread_prio) which is also equal to the priority of the > >rcutorture's > >> > > boost threads. Due to this the rcutorture test could starve the > >RCU threads > >> > > as well and defeat the boosting mechanism. I was able to solve a > >similar > >> > > issue by just passing rcutree.kthread_prio of 50 on the kernel > >command line. > >> > > > >> > > Paul, would it be ok if we changed the default kthread_prio to > >something > 1 > >> > > so that rcutorture can test properly without needing to pass any > >extra > >> > > rcutree.* parameters? > >> > > > >> > > so something like this in kernel/rcu/tree.c ? > >> > > > >> > > static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 2 : 0; > >> > > >> > Would it be possible to also condition this on rcutorture being > >built > >> > in? Or are they doing modprobes for rcutorture? > >> > >> They seem to be doing built-in rcutorture tests. But I believe the > >same > >> problem would occur even if you used modules? I believe the fact that > >> rcutorture is a module or built-in wouldn't matter to the underlying > >issue > >> which is the RCU subsystems's threads are at too low of a priority > >> (rcutree.kthread_prio = 1). > > > >Understood... > > > >> If you agree with changing the default priority, I have included a > >patch > >> below for rcu/dev. > > > >The problem is that without rcutorture, rcutree.kthread_prio=1 is a > >legitimate choice, and changing the default globally could be breaking > >someone. So it would be far better to up the priority only during > >known > >rcutorture testing. > > Oh I see what you're saying. I'll work on a patch along these lines > then. Thanks! Looking forward to seeing it! Thanx, Paul