From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755979AbcEYC03 (ORCPT ); Tue, 24 May 2016 22:26:29 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:60132 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755177AbcEYC01 (ORCPT ); Tue, 24 May 2016 22:26:27 -0400 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Tue, 24 May 2016 19:26:23 -0700 From: "Paul E. McKenney" To: Boqun Feng Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , fengguang.wu@intel.com Subject: Re: [PATCH] rcuperf: Don't treat gp_exp mis-setting as a WARN Message-ID: <20160525022623.GP4148@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1464139533-26551-1-git-send-email-boqun.feng@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464139533-26551-1-git-send-email-boqun.feng@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16052502-0021-0000-0000-000052206AF8 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 25, 2016 at 09:25:33AM +0800, Boqun Feng wrote: > 0day found a boot warning triggered in rcu_perf_writer() on !SMP kernel: > > WARN_ON(rcu_gp_is_normal() && gp_exp); > > , the root cause of which is trying to measure expedited grace > periods(by setting gp_exp to true by default) when all the grace periods > are normal(TINY RCU only has normal grace periods). > > However, such a mis-setting would only result in failing to measure the > performance for a specific kind of grace periods, therefore using a > WARN_ON to check this is a little overkilling. We could handle this > inside rcuperf module via some error messages to tell users about the > mis-settings. > > Therefore this patch removes the WARN_ON in rcu_perf_writer() and > handles those checkings in rcu_perf_init() with plain if() code. > > Moreover, this patch changes the default value of gp_exp to 1) align > with rcutorture tests and 2) make the default setting work for all RCU > implementations by default. > > Suggested-by: Paul E. McKenney > Signed-off-by: Boqun Feng > Fixes: http://lkml.kernel.org/r/57411b10.mFvG0+AgcrMXGtcj%fengguang.wu@intel.com Queued for review and testing, thank you! Thanx, Paul > --- > kernel/rcu/rcuperf.c | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c > index 3cee0d8393ed..8ce4eecff319 100644 > --- a/kernel/rcu/rcuperf.c > +++ b/kernel/rcu/rcuperf.c > @@ -58,7 +58,7 @@ MODULE_AUTHOR("Paul E. McKenney "); > #define VERBOSE_PERFOUT_ERRSTRING(s) \ > do { if (verbose) pr_alert("%s" PERF_FLAG "!!! %s\n", perf_type, s); } while (0) > > -torture_param(bool, gp_exp, true, "Use expedited GP wait primitives"); > +torture_param(bool, gp_exp, false, "Use expedited GP wait primitives"); > torture_param(int, holdoff, 10, "Holdoff time before test start (s)"); > torture_param(int, nreaders, -1, "Number of RCU reader threads"); > torture_param(int, nwriters, -1, "Number of RCU updater threads"); > @@ -363,8 +363,6 @@ rcu_perf_writer(void *arg) > u64 *wdpp = writer_durations[me]; > > VERBOSE_PERFOUT_STRING("rcu_perf_writer task started"); > - WARN_ON(rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp); > - WARN_ON(rcu_gp_is_normal() && gp_exp); > WARN_ON(!wdpp); > set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)); > sp.sched_priority = 1; > @@ -631,6 +629,16 @@ rcu_perf_init(void) > firsterr = -ENOMEM; > goto unwind; > } > + if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp) { > + VERBOSE_PERFOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!"); > + firsterr = -EINVAL; > + goto unwind; > + } > + if (rcu_gp_is_normal() && gp_exp) { > + VERBOSE_PERFOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!"); > + firsterr = -EINVAL; > + goto unwind; > + } > for (i = 0; i < nrealwriters; i++) { > writer_durations[i] = > kcalloc(MAX_MEAS, sizeof(*writer_durations[i]), > -- > 2.8.2 >