From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751979AbZKJFU5 (ORCPT ); Tue, 10 Nov 2009 00:20:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751901AbZKJFU4 (ORCPT ); Tue, 10 Nov 2009 00:20:56 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:41635 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751881AbZKJFUy (ORCPT ); Tue, 10 Nov 2009 00:20:54 -0500 Date: Tue, 10 Nov 2009 06:20:51 +0100 From: Ingo Molnar To: Aristeu Rozanski Cc: Thomas Gleixner , "H. Peter Anvin" , Peter Zijlstra , Fr?d?ric Weisbecker , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] x86: introduce NMI_AUTO as nmi_watchdog option Message-ID: <20091110052051.GJ7897@elte.hu> References: <20091103171054.GB25437@redhat.com> <20091104114630.GA16993@elte.hu> <20091104151929.GH18613@redhat.com> <20091104155641.GA11444@elte.hu> <20091109200201.GT18613@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091109200201.GT18613@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Aristeu Rozanski wrote: > > > > > NMI_AUTO is a new nmi_watchdog option that makes LAPIC be tried first > > > > > and if the CPU isn't supported, IOAPIC will be used. It's useful in > > > > > cases where NMI watchdog is enabled by default in a kernel built for > > > > > different machines. It can be configured by default or selected with > > > > > nmi_watchdog=3 or nmi_watchdog=auto parameters. > > > > > > > > What i'd like to see for the NMI watchdog is much more ambitious than > > > > this: the use of perf events to run a periodic NMI callback. > > > > > > > > The NMI watchdog would cause the creation of a per-cpu perf_event > > > > structure (in-kernel). All x86 CPUs that have perf event support (the > > > > majority of them) will thus be able to have an NMI watchdog using a > > > > nice, generic piece of code and we'd be able to phase out the open-coded > > > > NMI watchdog code. > > > > > > > > The user would not notice much from this: we'd still have the > > > > /proc/sys/kernel/nmi_watchdog toggle to turn it on/off, and we'd still > > > > have the nmi_watchog= boot parameter as well. But the underlying > > > > implementation would be far more generic and far more usable than the > > > > current code. > > > > > > > > Would you be interested in moving the NMI watchdog code in this > > > > direction? Most of the perf events changes (callbacks, helpers for > > > > in-kernel event allocations, etc.) are in latest -tip already, so you > > > > could use that as a base. > > > > > > but that would work only for LAPIC. You're suggesting killing IOAPIC > > > mode too? > > > > Would it be a big loss, with all modern systems expected to have a > > working lapic based NMI source? I wrote the IOAPIC mode originally but i > > dont feel too attached to it ;-) > > ok, fair enough. but since it'll be another implementation, do you > mind applying the patches I submitted so they can be used until the > new implementation is in place? For that i need to see at least an RFC v1 version series of the new implementation - otherwise we might end up sitting on this interim version with no-one doing the better variant. Thanks, Ingo