From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965487AbcBQTnR (ORCPT ); Wed, 17 Feb 2016 14:43:17 -0500 Received: from casper.infradead.org ([85.118.1.10]:35840 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965253AbcBQTnQ (ORCPT ); Wed, 17 Feb 2016 14:43:16 -0500 Date: Wed, 17 Feb 2016 20:43:12 +0100 From: Peter Zijlstra To: Oleg Nesterov Cc: Jiri Olsa , Pratyush Anand , Jeff Bastian , Michael Petlan , linux-kernel@vger.kernel.org Subject: Re: perf: wrong event->count report (Was: perf basic-test-aarch64 failures) Message-ID: <20160217194312.GN6357@twins.programming.kicks-ass.net> References: <20160211093047.GA12115@dhcp-0-82.del.redhat.com> <20160215070620.GA23850@dhcppc3.redhat.com> <20160217033416.GA7371@redhat.com> <20160217093539.GC10042@krava.brq.redhat.com> <20160217102555.GZ6357@twins.programming.kicks-ass.net> <20160217193442.GB14068@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160217193442.GB14068@redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 17, 2016 at 08:34:42PM +0100, Oleg Nesterov wrote: > On 02/17, Peter Zijlstra wrote: > > > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -3173,6 +3173,10 @@ static void perf_event_enable_on_exec(in > > > > cpuctx = __get_cpu_context(ctx); > > perf_ctx_lock(cpuctx, ctx); > > + > > + update_context_time(ctx); > > + update_cgrp_time_from_cpuctx(cpuctx); > > + > > Even if I don't really understand this change I agree, probably we need to update > the counters for enable_on_exec events somehow. But I don't see how this change can > make total_time_running == total_time_enabled. Yes, to get them exactly equal more is needed. But I suspect the very small difference generated here is practically irrelevant. Making them equal requires some very careful auditing, but is otherwise entirely possible. The bigger problem seems to be that this (seemingly) simple change makes Jiri's machine explode, I yet have to look at reproducing that.