From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756809Ab0LAT64 (ORCPT ); Wed, 1 Dec 2010 14:58:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:18057 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754784Ab0LAT6z (ORCPT ); Wed, 1 Dec 2010 14:58:55 -0500 Date: Wed, 1 Dec 2010 14:58:35 -0500 From: Vivek Goyal To: Peter Zijlstra Cc: Yinghai Lu , Ingo Molnar , Jason Wessel , Don Zickus , "linux-kernel@vger.kernel.org" , Haren Myneni , "Eric W. Biederman" Subject: Re: perf hw in kexeced kernel broken in tip Message-ID: <20101201195835.GE2511@redhat.com> References: <4CF60095.1020900@kernel.org> <1291202867.4023.3.camel@twins> <20101201160640.GA2511@redhat.com> <1291219906.32004.1671.camel@laptop> <20101201162335.GB2511@redhat.com> <1291232292.32004.1969.camel@laptop> <20101201194644.GD2511@redhat.com> <1291232989.32004.1987.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1291232989.32004.1987.camel@laptop> 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 On Wed, Dec 01, 2010 at 08:49:49PM +0100, Peter Zijlstra wrote: > On Wed, 2010-12-01 at 14:46 -0500, Vivek Goyal wrote: > > On Wed, Dec 01, 2010 at 08:38:12PM +0100, Peter Zijlstra wrote: > > > On Wed, 2010-12-01 at 11:23 -0500, Vivek Goyal wrote: > > > > > What does kexec normally do to ensure hardware is left in a sane state? > > > > > > > > Typically calls device_shutdown() and sysdev_shutdown() from > > > > kernel_restart_prepare() to shutdown the devices. > > > > > > > > Also calls machine_shutdown() which depending on architecture can take > > > > care of various things like stopping other cpus, shutting down LAPIC, > > > > disabling IOAPIC, disabling hpet, shutting down IOMMU etc > > > > (native_machine_shutdown()). > > > > > > So basically there's no sane generic reset callout? > > > > I think ->shutdown() calls are sane generic callouts. Isn't it? > > ->shutdown looks like it's about to reset/halt the hardware, no point in > slowing down the regular shutdown/reboot path for something like this, > we know the hardware will get reset to a sane state. I think we already call ->shutdown() in regular reboot path. kernel_restart() kernel_restart_prepare() device_shutdown(); sysdev_shutdown(); So it should not make lot of difference if perf subsystem/counters are also shutdown using ->shutdown(). > > > There seem to be few exceptions for LAPIC, IOMMU and HPET and I am not > > sure why they are not covered by shutdown calls. CCing Eric, he might > > have more insight into it. > > That's all arch specific, but even there I don't think the reset code > should live outside of kexec. I would not know the history but I have heard stories that if you don't shutdown the hardware over restart, BIOS might not be expecting it and might get trumped. Thanks Vivek