Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932923AbdCGPXV (ORCPT ); Tue, 7 Mar 2017 10:23:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59616 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932849AbdCGPWh (ORCPT ); Tue, 7 Mar 2017 10:22:37 -0500 Date: Tue, 7 Mar 2017 10:22:06 -0500 From: Don Zickus To: Ingo Molnar Cc: Mike Travis , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Peter Zijlstra , Dimitri Sivanich , Frank Ramsay , Russ Anderson , Tony Ernst , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] x86/platform: Add a low priority low frequency NMI call chain Message-ID: <20170307152206.4nqqrekwmfqbdn7b@redhat.com> References: <20170306181737.059578494@asylum.americas.sgi.com> <20170306181737.322206440@asylum.americas.sgi.com> <20170307074210.GA24782@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170307074210.GA24782@gmail.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Tue, 07 Mar 2017 15:22:10 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1600 Lines: 41 On Tue, Mar 07, 2017 at 08:42:10AM +0100, Ingo Molnar wrote: > > * Mike Travis wrote: > > > Add a new NMI call chain that is called last after all other NMI handlers > > have been checked and did not "handle" the NMI. This mimics the current > > NMI_UNKNOWN call chain except it eliminates the WARNING message about > > multiple NMI handlers registering on this call chain. > > > > This call chain dramatically lowers the NMI call frequency when high > > frequency NMI tools are in use, notably the perf tools. It is required > > for NMI handlers that cannot sustain a high NMI call rate without > > ramifications to the system operability. > > So how about we just turn off that warning instead? I don't remember the last time > it actually _helped_ us find any kernel or hardware bug - and it has caused tons > of problems... Yeah, that is one way to solve it. :-) Originally I put that in there because the unknown nmi handlers sometime do not return, making it impossible for the second handler to run. But you are right, it probably hasn't really helped find any problems. I wasn't aware of problems it was causing (not that I was looking through emails to find them either). Cheers, Don > > It's not like we warn about excess regular IRQs either - we either handle them or > at most increase a counter somewhere. We could do the same for NMIs: introduce a > counter somewhere that counts the number of seemingly unhandled NMIs. > > But in any case, we should not spam the kernel log, neither with high, nor with > low frequency. > > Thanks, > > Ingo