From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xHvqM01y0zDrD6 for ; Thu, 27 Jul 2017 11:42:22 +1000 (AEST) Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v6R1ctLc080710 for ; Wed, 26 Jul 2017 21:42:20 -0400 Received: from e15.ny.us.ibm.com (e15.ny.us.ibm.com [129.33.205.205]) by mx0a-001b2d01.pphosted.com with ESMTP id 2by4fxwafp-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 26 Jul 2017 21:42:20 -0400 Received: from localhost by e15.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 26 Jul 2017 21:42:19 -0400 Date: Wed, 26 Jul 2017 18:42:14 -0700 From: "Paul E. McKenney" To: David Miller Cc: Jonathan.Cameron@huawei.com, dzickus@redhat.com, sfr@canb.auug.org.au, linuxarm@huawei.com, npiggin@gmail.com, abdhalee@linux.vnet.ibm.com, sparclinux@vger.kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org Subject: Re: RCU lockup issues when CONFIG_SOFTLOCKUP_DETECTOR=n - any one else seeing this? Reply-To: paulmck@linux.vnet.ibm.com References: <20170726223658.GA27617@linux.vnet.ibm.com> <20170726.154540.150558937277891719.davem@davemloft.net> <20170726231505.GG3730@linux.vnet.ibm.com> <20170726.162200.1904949371593276937.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170726.162200.1904949371593276937.davem@davemloft.net> Message-Id: <20170727014214.GH3730@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Jul 26, 2017 at 04:22:00PM -0700, David Miller wrote: > From: "Paul E. McKenney" > Date: Wed, 26 Jul 2017 16:15:05 -0700 > > > On Wed, Jul 26, 2017 at 03:45:40PM -0700, David Miller wrote: > >> Just out of curiousity, what x86 idle method is your machine using? > >> The mwait one or the one which simply uses 'halt'? The mwait variant > >> might mask this bug, and halt would be a lot closer to how sparc64 and > >> Jonathan's system operates. > > > > My kernel builds with CONFIG_INTEL_IDLE=n, which I believe means that > > I am not using the mwait one. Here is a grep for IDLE in my .config: > > > > CONFIG_NO_HZ_IDLE=y > > CONFIG_GENERIC_SMP_IDLE_THREAD=y > > # CONFIG_IDLE_PAGE_TRACKING is not set > > CONFIG_ACPI_PROCESSOR_IDLE=y > > CONFIG_CPU_IDLE=y > > # CONFIG_CPU_IDLE_GOV_LADDER is not set > > CONFIG_CPU_IDLE_GOV_MENU=y > > # CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED is not set > > # CONFIG_INTEL_IDLE is not set > > No, that doesn't influence it. It is determined by cpu features at > run time. > > If you are using mwait, it'll say so in your kernel log like this: > > using mwait in idle threads Thank you for the hint! And vim says: "E486: Pattern not found: using mwait in idle threads" > >> On sparc64 the cpu yield we do in the idle loop sleeps the cpu. It's > >> local TICK register keeps advancing, and the local timer therefore > >> will still trigger. Also, any externally generated interrupts > >> (including cross calls) will wake up the cpu as well. > >> > >> The tick-sched code is really tricky wrt. NO_HZ even in the NO_HZ_IDLE > >> case. One of my running theories is that we miss scheduling a tick > >> due to a race. That would be consistent with the behavior we see > >> in the RCU dumps, I think. > > > > But wouldn't you have to miss a -lot- of ticks to get an RCU CPU stall > > warning? By default, your grace period needs to extend for more than > > 21 seconds (more than one-third of a -minute-) to get one. Or do > > you mean that the ticks get shut off now and forever, as opposed to > > just losing one of them? > > Hmmm, good point. And I was talking about simply missing one tick. > > Indeed, that really wouldn't explain how we end up with a RCU stall > dump listing almost all of the cpus as having missed a grace period. I have seen stranger things, but admittedly not often. Thanx, Paul