From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755426Ab0LAVsY (ORCPT ); Wed, 1 Dec 2010 16:48:24 -0500 Received: from out02.mta.xmission.com ([166.70.13.232]:43622 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754797Ab0LAVsX (ORCPT ); Wed, 1 Dec 2010 16:48:23 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Peter Zijlstra Cc: Vivek Goyal , Yinghai Lu , Ingo Molnar , Jason Wessel , Don Zickus , "linux-kernel\@vger.kernel.org" , Haren Myneni 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> <20101201195835.GE2511@redhat.com> <1291234036.32004.2008.camel@laptop> Date: Wed, 01 Dec 2010 13:48:07 -0800 In-Reply-To: <1291234036.32004.2008.camel@laptop> (Peter Zijlstra's message of "Wed, 01 Dec 2010 21:07:16 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in01.mta.xmission.com;;;ip=98.207.157.188;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19Q5OH3SEIe+LECm4rt8pV9J2VijIYp/Cc= X-SA-Exim-Connect-IP: 98.207.157.188 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * 7.0 XM_URI_RBL URI blacklisted in uri.bl.xmission.com * [URIs: infradead.org] * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa05 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_XMDrugObfuBody_08 obfuscated drug references * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay X-Spam-DCC: XMission; sa05 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ***;Peter Zijlstra X-Spam-Relay-Country: Subject: Re: perf hw in kexeced kernel broken in tip X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Fri, 06 Aug 2010 16:31:04 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra writes: > On Wed, 2010-12-01 at 14:58 -0500, Vivek Goyal wrote: >> 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(). > > Oh, but I'm not a device or sysdev thing, I'll never get something like > that. There is also the reboot notifier, if the NMI needs to be controlled outside of device model. Sigh. The NMI handling is such a special case. >> > > 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. > > Never yet had a problem with that. I haven't personally but I have certainly heard stories and seen debugging sessions where some devices work or don't depending on the order of running linux and windows on a machine, with soft reboots in between. Eric