From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757647Ab0HDKEl (ORCPT ); Wed, 4 Aug 2010 06:04:41 -0400 Received: from tx2ehsobe004.messaging.microsoft.com ([65.55.88.14]:40272 "EHLO TX2EHSOBE008.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756983Ab0HDKEj (ORCPT ); Wed, 4 Aug 2010 06:04:39 -0400 X-SpamScore: -16 X-BigFish: VPS-16(zz1432N98dN936eMzz1202hzzz32i2a8h64h) X-Spam-TCS-SCL: 3:0 X-WSS-ID: 0L6MH63-02-23G-02 X-M-MSG: Date: Wed, 4 Aug 2010 12:01:16 +0200 From: Robert Richter To: Lin Ming CC: Ingo Molnar , Peter Zijlstra , Don Zickus , Cyrill Gorcunov , "fweisbec@gmail.com" , "linux-kernel@vger.kernel.org" , "Huang, Ying" Subject: Re: A question of perf NMI handler Message-ID: <20100804100116.GH26154@erda.amd.com> References: <1280913670.20797.179.camel@minggr.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1280913670.20797.179.camel@minggr.sh.intel.com> User-Agent: Mutt/1.5.20 (2009-06-14) X-Reverse-DNS: ausb3extmailp02.amd.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04.08.10 05:21:10, Lin Ming wrote: > With nmi_watchdog enabled, perf_event_nmi_handler always return > NOTIFY_STOP(active_events > 0), and the notifier call chain will not > call further. > > If it was not perf NMI, does the perf nmi handler may stop the real NMI > handler get called because NOTIFY_STOP is returned?? There is no general mechanism for recording the NMI source (except if it was external triggered, e.g. by the southbridge). Also, all nmis are mapped to NMI vector 2 and therefore there is no way to find out the reason by using apic mask registers. Now, if multiple perfctrs trigger an nmi, it may happen that a handler has nothing to do because the counter was already handled by the previous one. Thus, it is valid to have unhandled nmis caused by perfctrs. So, with counters enabled we always have to return stop for *all* nmis as we cannot detect that it was an perfctr nmi. Otherwise we could trigger an unhandled nmi. To ensure that all other nmi handlers are called, the perfctr's nmi handler must have the lowest priority. Then, the handler will be the last in the chain. -Robert -- Advanced Micro Devices, Inc. Operating System Research Center