Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759620Ab2BOJcN (ORCPT ); Wed, 15 Feb 2012 04:32:13 -0500 Received: from mail-pz0-f46.google.com ([209.85.210.46]:63827 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753505Ab2BOJcJ (ORCPT ); Wed, 15 Feb 2012 04:32:09 -0500 Date: Wed, 15 Feb 2012 01:32:04 -0800 From: Steven Noonan To: Peter Zijlstra Cc: Ben Guthro , Konrad Rzeszutek Wilk , linux-kernel@vger.kernel.org, Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo , Jeremy Fitzhardinge Subject: Re: bisected: 'perf top' causing soft lockups under Xen Message-ID: <20120215093204.GA17286@asmodeus> References: <1328894901.25989.20.camel@laptop> <20120210190412.GB12975@phenom.dumpdata.com> <20120212205016.GA2794@asmodeus> <20120215085737.GA13722@asmodeus> <1329297944.2293.36.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1329297944.2293.36.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1362 Lines: 34 On Wed, Feb 15, 2012 at 10:25:44AM +0100, Peter Zijlstra wrote: > On Wed, 2012-02-15 at 00:57 -0800, Steven Noonan wrote: > > It seems to me that there are two options for fixing this, but I'm > > probably lacking the necessary context (or experience with Xen). Either: > > > > - The patch provided by Ben needs to have additional work to specially > > handle IRQ_WORK_VECTOR, since it seems to be a special case where > > there's no event channel attached for it. Perhaps adding an event > > channel for this is the fix? Seems high-overhead, but I lack a good > > understanding of how interrupts are handled in Xen. > > So that's a self-IPI, is Xen failing to implement this? Yes. Ben's patch implements it, but it explodes (NULL pointer dereference) when it can't find an event channel for IRQ_WORK_VECTOR. > > > or > > > > - Perf needs to be "enlightened" about Xen and avoid sending an IPI in > > the first place. > > Uhm, no. If anything Xen should simply not implement > arch_irq_work_raise(). The callbacks are then ran from the timer > interrupt. Sorry, wild guess. I'm a kernel newbie. :) -- 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/