From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754298Ab1JJSqF (ORCPT ); Mon, 10 Oct 2011 14:46:05 -0400 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:38093 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753706Ab1JJSqC (ORCPT ); Mon, 10 Oct 2011 14:46:02 -0400 Message-ID: <4E933D5C.3040803@linux.vnet.ibm.com> Date: Tue, 11 Oct 2011 00:15:48 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux i686; rv:7.0) Gecko/20110927 Thunderbird/7.0 MIME-Version: 1.0 To: Borislav Petkov CC: "tj@kernel.org" , Alan Stern , "rjw@sisk.pl" , "pavel@ucw.cz" , "len.brown@intel.com" , "mingo@elte.hu" , "a.p.zijlstra@chello.nl" , "akpm@linux-foundation.org" , "suresh.b.siddha@intel.com" , "lucas.demarchi@profusion.mobi" , "rusty@rustcorp.com.au" , "rdunlap@xenotime.net" , "vatsa@linux.vnet.ibm.com" , "ashok.raj@intel.com" , "tigran@aivazian.fsnet.co.uk" , "tglx@linutronix.de" , "hpa@zytor.com" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-doc@vger.kernel.org" Subject: Re: [PATCH v2 0/3] Freezer, CPU hotplug, x86 Microcode: Fix task freezing failures References: <4E931018.8030904@linux.vnet.ibm.com> <20111010165343.GA29261@aftab> <4E932BBA.9090501@linux.vnet.ibm.com> <20111010175336.GA29415@aftab> <20111010180848.GI8100@google.com> <20111010183442.GC29415@aftab> In-Reply-To: <20111010183442.GC29415@aftab> 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 On 10/11/2011 12:04 AM, Borislav Petkov wrote: > Hi Tejun, > > On Mon, Oct 10, 2011 at 02:08:48PM -0400, tj@kernel.org wrote: >> Maybe I'm confused but is that patch correct for actual CPU hotplug >> case? If not, what's the point in doing that? What are we gonna do >> after six month some people come up with "CPU hotplug fails to load >> new microcode for the new CPU"? > [...] > >> If somebody is sure that microcode don't need to be changed once >> loaded, then all's good and dandy but that's not the case here, right? > > Well, basically the current situation didn't change the ucode - it > simply reloaded the same image from before going offline. > > See, there's this another problem with what we have right now: imagine > you've just updated the ucode image on disk and offline only a subset of > the cores. Then you online them again and they now get the newer ucode > image while the others still run the old ucode. This could explode or > could not, one thing's for sure: all bets are off. If we don't reload it > on hotplug, we're fine - only module reload triggers the ucode update in > a fairly synchronized manner. > This one makes a lot of sense to me. I hadn't thought of it before. >> If you want to optimize away microcode unloading during >> suspend/resume, the RTTD is doing revalidation / reload during >> CPU_ONLINE as necessary. > > see above. > >> If this use case doesn't really matter too much to anyone, just >> leaving it alone would be better than adding band aid which can lead >> to very obscure issues down the road (oooh, that microcode shouldn't >> have been loaded to that cpu). > > I'd like to actually hear someone justify such a requirement. > > I hope I'm making some sense here. > -- Regards, Srivatsa S. Bhat Linux Technology Center, IBM India Systems and Technology Lab