From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751833AbaHOF0B (ORCPT ); Fri, 15 Aug 2014 01:26:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:16204 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750725AbaHOF0A (ORCPT ); Fri, 15 Aug 2014 01:26:00 -0400 Date: Fri, 15 Aug 2014 10:54:11 +0530 From: Amit Shah To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, riel@redhat.com, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu Subject: Re: [PATCH tip/core/rcu 1/2] rcu: Parallelize and economize NOCB kthread wakeups Message-ID: <20140815052411.GF1934@grmbl.mre> References: <20140811201102.GD5821@linux.vnet.ibm.com> <20140811201845.GG4184@grmbl.mre> <20140811203421.GE5821@linux.vnet.ibm.com> <20140812034531.GA13801@linux.vnet.ibm.com> <20140812053321.GK4184@grmbl.mre> <20140812160621.GC4752@linux.vnet.ibm.com> <20140812213936.GA3106@linux.vnet.ibm.com> <20140812214151.GB3106@linux.vnet.ibm.com> <20140813054439.GA29913@grmbl.mre> <20140813130049.GS4752@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140813130049.GS4752@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (Wed) 13 Aug 2014 [06:00:49], Paul E. McKenney wrote: > On Wed, Aug 13, 2014 at 11:14:39AM +0530, Amit Shah wrote: > > On (Tue) 12 Aug 2014 [14:41:51], Paul E. McKenney wrote: > > > On Tue, Aug 12, 2014 at 02:39:36PM -0700, Paul E. McKenney wrote: > > > > On Tue, Aug 12, 2014 at 09:06:21AM -0700, Paul E. McKenney wrote: > > > > > On Tue, Aug 12, 2014 at 11:03:21AM +0530, Amit Shah wrote: > > > > > > > > [ . . . ] > > > > > > > > > > I know of only virtio-console doing this (via userspace only, > > > > > > though). > > > > > > > > > > As in userspace within the guest? That would not work. The userspace > > > > > that the qemu is running in might. There is a way to extract ftrace info > > > > > from crash dumps, so one approach would be "sendkey alt-sysrq-c", then > > > > > pull the buffer from the resulting dump. For all I know, there might also > > > > > be some script that uses the qemu "x" command to get at the ftrace buffer. > > > > > > > > > > Again, I cannot reproduce this, and I have been through the code several > > > > > times over the past few days, and am not seeing it. I could start > > > > > sending you random diagnostic patches, but it would be much better if > > > > > we could get the trace data from the failure. > > > > I think the only recourse I now have is to dump the guest state from > > qemu, and attempt to find the ftrace buffers by poking pages and > > finding some ftrace-like struct... and then dumping the buffers. > > The data exists in the qemu guest state, so it would be good to have > it one way or another. My current (perhaps self-serving) guess is that > you have come up with a way to trick qemu into dropping IPIs. I didn't get around to doing this yet; will get to it next week. In the meantime, I tried this on RHEL6 (with RHEL6 qemu and gcc and seabios), and that exhibits the problem similarly with my .config. > > > + > > > return true; > > > > I have return 1; here. > > > > I'm on linux.git, c8d6637d0497d62093dbba0694c7b3a80b79bfe1. > > I am working on top of my -rcu tree, which contains the fix from "1" to > "true" compared to current mainline. So this will resolve itself, and > you should be OK fixing up conflict in either direction. Yep, I did do that. Just noted here that the hunk didn't directly apply. Thanks, Amit