Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756813Ab2HFRZ0 (ORCPT ); Mon, 6 Aug 2012 13:25:26 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:50754 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753721Ab2HFRZZ (ORCPT ); Mon, 6 Aug 2012 13:25:25 -0400 Message-ID: <501FFD2A.4010905@us.ibm.com> Date: Mon, 06 Aug 2012 10:21:46 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120714 Thunderbird/14.0 MIME-Version: 1.0 To: Sasha Levin CC: Avi Kivity , paulmck@linux.vnet.ibm.com, "linux-kernel@vger.kernel.org" , mingo@kernel.org, a.p.zijlstra@chello.nl, prarit@redhat.com, tglx@linutronix.de Subject: Re: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6 References: <500ED719.2010002@gmail.com> <50112D3B.4020201@redhat.com> <50127B16.5040401@gmail.com> <50153138.4020304@redhat.com> <5015A5A8.7030601@gmail.com> <50161D5E.4030009@redhat.com> <50165046.9020705@gmail.com> <501654D3.7020504@redhat.com> <50168162.4010508@gmail.com> <50168981.3000001@redhat.com> <501EA58D.4090606@gmail.com> In-Reply-To: <501EA58D.4090606@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12080617-6078-0000-0000-00000DF08845 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1573 Lines: 40 On 08/05/2012 09:55 AM, Sasha Levin wrote: > On 07/30/2012 03:17 PM, Avi Kivity wrote: >> Possible causes: >> - the APIC calibration in the guest failed, so it is programming too >> low values into the timer >> - it actually needs 1 us wakeups and then can't keep up (esp. as kvm >> interrupt injection is slowing it down) >> >> You can try to find out by changing >> arch/x86/kvm/lapic.c:start_lapic_timer() to impose a minimum wakeup of >> (say) 20 microseconds which will let the guest live long enough for you >> to ftrace it and see what kind of timers it is programming. > I've kept trying to narrow it down, and found out It's triggerable using adjtimex(). > > At that point I've bisected it, and got the following commit (parties Cc'ed): > > commit 5baefd6d84163443215f4a99f6a20f054ef11236 > Author: John Stultz > Date: Tue Jul 10 18:43:25 2012 -0400 > > hrtimer: Update hrtimer base offsets each hrtimer_interrupt > > > I've also confirmed that reverting the commit above on top of linux-next indeed fixes the issue. Hey Sasha, Thanks for the heads up. I don't have a clear sense of what could be wrong here yet, but if you see this with 3.6-rc but not 3.5, could you try the fix(1d17d17484d40f2d5b35c79518597a2b25296996) Ingo just made on tip/timers/urgent? thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/