Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754837Ab2HEQzK (ORCPT ); Sun, 5 Aug 2012 12:55:10 -0400 Received: from mail-ob0-f174.google.com ([209.85.214.174]:47194 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754175Ab2HEQzH (ORCPT ); Sun, 5 Aug 2012 12:55:07 -0400 Message-ID: <501EA58D.4090606@gmail.com> Date: Sun, 05 Aug 2012 18:55:41 +0200 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120730 Thunderbird/14.0 MIME-Version: 1.0 To: Avi Kivity CC: paulmck@linux.vnet.ibm.com, "linux-kernel@vger.kernel.org" , johnstul@us.ibm.com, 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> In-Reply-To: <50168981.3000001@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1229 Lines: 29 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. -- 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/