From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757841Ab0EKU14 (ORCPT ); Tue, 11 May 2010 16:27:56 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:41199 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753078Ab0EKU1y (ORCPT ); Tue, 11 May 2010 16:27:54 -0400 Subject: Re: [BUG] perf_event: when events are grouped, the time enabled / running values are incorrect From: Peter Zijlstra To: Stephane Eranian Cc: eranian@gmail.com, Corey Ashford , LKML , Paul Mackerras In-Reply-To: References: <4BE4C4BF.6020801@linux.vnet.ibm.com> <1273588935.1810.6.camel@laptop> <1273608676.1810.61.camel@laptop> Content-Type: text/plain; charset="UTF-8" Date: Tue, 11 May 2010 22:27:51 +0200 Message-ID: <1273609671.1810.74.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2010-05-11 at 22:23 +0200, Stephane Eranian wrote: > On Tue, May 11, 2010 at 10:11 PM, Peter Zijlstra wrote: > > On Tue, 2010-05-11 at 21:55 +0200, stephane eranian wrote: > >> Events are also grouped in this example. Both this same issue exists > >> also when only > >> one event is used. I suspect an update_event_times() or > >> update_group_times() is also > >> missing on the sampling path in perf_overflow_handler(). > > > > Hrmm, you're right, except fixing that is non-trivial. > > update_event_times() wants to be called with ctx->lock held and we can't > > do that from NMI context. > > > Why do you need the lock when the event is running on a CPU in NMI context? > What action issued remotely could modify the data used by this function without > the need for IPI? Not sure, would at the very least have to verify that. I'll try and have a look.