From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753216Ab2IZWqP (ORCPT ); Wed, 26 Sep 2012 18:46:15 -0400 Received: from mga03.intel.com ([143.182.124.21]:58037 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752863Ab2IZWqO (ORCPT ); Wed, 26 Sep 2012 18:46:14 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.80,492,1344236400"; d="scan'208";a="149570800" Subject: Re: [PATCH RESEND] x86/fixup_irq: Clean the offlining CPU from the irq affinity mask From: Suresh Siddha Reply-To: Suresh Siddha To: "Srivatsa S. Bhat" Cc: Chuansheng Liu , tglx@linutronix.de, mingo@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org, yanmin_zhang@linux.intel.com, "Paul E. McKenney" , Peter Zijlstra , "rusty@rustcorp.com.au" Date: Wed, 26 Sep 2012 15:46:27 -0700 In-Reply-To: <50633BA0.5030700@linux.vnet.ibm.com> References: <1348681092.19514.10.camel@cliu38-desktop-build> <1348703122.19514.17.camel@cliu38-desktop-build> <50632767.5050607@linux.vnet.ibm.com> <1348679199.26695.455.camel@sbsiddha-desk.sc.intel.com> <50633BA0.5030700@linux.vnet.ibm.com> Organization: Intel Corp Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.0.3 (3.0.3-1.fc15) Content-Transfer-Encoding: 7bit Message-ID: <1348699588.6644.21.camel@sbsiddha-desk.sc.intel.com> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2012-09-26 at 23:00 +0530, Srivatsa S. Bhat wrote: > On 09/26/2012 10:36 PM, Suresh Siddha wrote: > > On Wed, 2012-09-26 at 21:33 +0530, Srivatsa S. Bhat wrote: > >> I have some fundamental questions here: > >> 1. Why was the CPU never removed from the affinity masks in the original > >> code? I find it hard to believe that it was just an oversight, because the > >> whole point of fixup_irqs() is to affine the interrupts to other CPUs, IIUC. > >> So, is that really a bug or is the existing code correct for some reason > >> which I don't know of? > > > > I am not aware of the history but my guess is that the affinity mask > > which is coming from the user-space wants to be preserved. And > > fixup_irqs() is fixing the underlying interrupt routing when the cpu > > goes down > > and the code that corresponds to that is: > irq_force_complete_move(irq); is it? No. irq_set_affinity() > > with a hope that things will be corrected when the cpu comes > > back online. But as Liu noted, we are not correcting the underlying > > routing when the cpu comes back online. I think we should fix that > > rather than modifying the user-specified affinity. > > > > Hmm, I didn't entirely get your suggestion. Are you saying that we should change > data->affinity (by calling ->irq_set_affinity()) during offline but maintain a > copy of the original affinity mask somewhere, so that we can try to match it > when possible (ie., when CPU comes back online)? Don't change the data->affinity in the fixup_irqs() and shortly after a cpu is online, call irq_chip's irq_set_affinity() for those irq's who affinity included this cpu (now that the cpu is back online, irq_set_affinity() will setup the HW routing tables correctly). This presumes that across the suspend/resume, cpu offline/online operations, we don't want to break the irq affinity setup by the user-level entity like irqbalance etc... > > That happens only if the irq chip doesn't have the irq_set_affinity() setup. > > That is my other point of concern : setting irq affinity can fail even if > we have ->irq_set_affinity(). (If __ioapic_set_affinity() fails, for example). > Why don't we complain in that case? I think we should... and if its serious > enough, abort the hotplug operation or atleast indicate that offline failed.. yes if there is a failure then we are in trouble, as the cpu is already disappeared from the online-masks etc. For platforms with interrupt-remapping, interrupts can be migrated from the process context and as such this all can be done much before. And for legacy platforms we have done quite a few changes in the recent past like using eoi_ioapic_irq() for level triggered interrupts etc, that makes it as safe as it can be. Perhaps we can move most of the fixup_irqs() code much ahead and the lost section of the current fixup_irqs() (which check IRR bits and use the retrigger function to trigger the interrupt on another cpu) can still be done late just like now. thanks, suresh