From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752839AbcBWPs4 (ORCPT ); Tue, 23 Feb 2016 10:48:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41055 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752373AbcBWPsy (ORCPT ); Tue, 23 Feb 2016 10:48:54 -0500 Date: Tue, 23 Feb 2016 16:48:49 +0100 From: Jiri Olsa To: Peter Zijlstra Cc: mingo@kernel.org, alexander.shishkin@linux.intel.com, eranian@google.com, linux-kernel@vger.kernel.org, vince@deater.net, dvyukov@google.com, andi@firstfloor.org, sasha.levin@oracle.com, oleg@redhat.com, Pratyush Anand Subject: Re: [RFC][PATCH 4/7] perf: Fix scaling vs enable_on_exec Message-ID: <20160223154849.GC9102@krava.redhat.com> References: <20160219143743.692339502@infradead.org> <20160219144132.043429490@infradead.org> <20160223152729.GT6357@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160223152729.GT6357@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 23 Feb 2016 15:48:54 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 23, 2016 at 04:27:29PM +0100, Peter Zijlstra wrote: > On Fri, Feb 19, 2016 at 03:37:47PM +0100, Peter Zijlstra wrote: > > Oleg reported that enable_on_exec results in weird scale factors. > > > > The recent commit 3e349507d12d ("perf: Fix perf_enable_on_exec() event > > scheduling") caused this by moving task_ctx_sched_out() from before > > __perf_event_mask_enable() to after it. > > > > The overlooked concequence of that change is that task_ctx_sched_out() > > would update the ctx time fields, and now __perf_event_mask_enable() > > uses stale time. > > > > Fix this by adding an explicit time update. > > > > While looking at this, I also found that we need an ctx->is_active > > check in perf_install_in_context(). > > > > XXX: does this actually fix the reported issue? I'm not sure what the > > reproduction case is. Also an earlier version made Jiri's machine > > explode -- something I've not managed to reproduce either. > > Jiri, can you have a look at this and perhaps share the reproducer? yep, I'm testing this patchset, but got stuck with 'crash' tool to get some reasonable output.. got stuck on unrelated sched deadlock ;-) the reproducer is described in this email: http://marc.info/?l=linux-kernel&m=145568006709552&w=2 CC-ing Pratyush jjirka