From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754202AbcBWP3e (ORCPT ); Tue, 23 Feb 2016 10:29:34 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:47267 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752981AbcBWP1p (ORCPT ); Tue, 23 Feb 2016 10:27:45 -0500 Date: Tue, 23 Feb 2016 16:27:29 +0100 From: Peter Zijlstra To: mingo@kernel.org, alexander.shishkin@linux.intel.com, eranian@google.com Cc: linux-kernel@vger.kernel.org, vince@deater.net, dvyukov@google.com, andi@firstfloor.org, jolsa@redhat.com, sasha.levin@oracle.com, oleg@redhat.com Subject: Re: [RFC][PATCH 4/7] perf: Fix scaling vs enable_on_exec Message-ID: <20160223152729.GT6357@twins.programming.kicks-ass.net> References: <20160219143743.692339502@infradead.org> <20160219144132.043429490@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160219144132.043429490@infradead.org> 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 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? > Fixes: 3e349507d12d ("perf: Fix perf_enable_on_exec() event scheduling") > Reported-by: Oleg Nesterov > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/events/core.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -2170,12 +2170,12 @@ perf_install_in_context(struct perf_even > raw_spin_unlock_irq(&ctx->lock); > return; > } > - update_context_time(ctx); > - /* > - * Update cgrp time only if current cgrp matches event->cgrp. > - * Must be done before calling add_event_to_ctx(). > - */ > - update_cgrp_time_from_event(event); > + > + if (ctx->is_active) { > + update_context_time(ctx); > + update_cgrp_time_from_event(event); > + } > + > add_event_to_ctx(event, ctx); > raw_spin_unlock_irq(&ctx->lock); > > @@ -3122,6 +3122,12 @@ static void perf_event_enable_on_exec(in > > cpuctx = __get_cpu_context(ctx); > perf_ctx_lock(cpuctx, ctx); > + > + if (ctx->is_active) { > + update_context_time(ctx); > + update_cgrp_time_from_cpuctx(cpuctx); > + } > + > list_for_each_entry(event, &ctx->event_list, event_entry) > enabled |= event_enable_on_exec(event, ctx); > > >