From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965563AbbEMU6q (ORCPT ); Wed, 13 May 2015 16:58:46 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:37311 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965288AbbEMU6h (ORCPT ); Wed, 13 May 2015 16:58:37 -0400 Date: Wed, 13 May 2015 10:23:38 -0700 From: "Paul E. McKenney" To: josh@joshtriplett.org Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH tip/core/rcu 04/13] rcutorture: Allow negative values of nreaders to oversubscribe Message-ID: <20150513172338.GI6776@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20150512225753.GA5012@linux.vnet.ibm.com> <1431471493-5431-1-git-send-email-paulmck@linux.vnet.ibm.com> <1431471493-5431-4-git-send-email-paulmck@linux.vnet.ibm.com> <20150513010313.GF14292@cloud> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150513010313.GF14292@cloud> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15051320-0033-0000-0000-000004811CCC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 12, 2015 at 06:03:13PM -0700, josh@joshtriplett.org wrote: > On Tue, May 12, 2015 at 03:58:04PM -0700, Paul E. McKenney wrote: > > From: "Paul E. McKenney" > > > > By default, with rcutorture.nreaders equal to -1, rcutorture provisions > > N-1 reader kthreads, where N is the number of CPUs. This avoids > > rcutorture-induced stalls, but also avoids heavier levels of torture. > > This commit therefore allows negative values of rcutorture.nreaders > > to specify larger numbers of reader kthreads, so that for example > > rcutorture.nreaders=-2 provisions N kthreads and rcutorture.nreaders=-5 > > provisions N+3 kthreads. > > > > Signed-off-by: Paul E. McKenney > > That seems rather excessively arcane. Then again, I guess we started > down the road to arcana when we allowed -1 to mean N-1. Indeed... > However, could you please document this in the module parameter > documentation? Good point, fixed! Thanx, Paul > > kernel/rcu/rcutorture.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c > > index a67ef6ff86b0..7294d605c481 100644 > > --- a/kernel/rcu/rcutorture.c > > +++ b/kernel/rcu/rcutorture.c > > @@ -1701,7 +1701,7 @@ rcu_torture_init(void) > > if (nreaders >= 0) { > > nrealreaders = nreaders; > > } else { > > - nrealreaders = num_online_cpus() - 1; > > + nrealreaders = num_online_cpus() - 2 - nreaders; > > if (nrealreaders <= 0) > > nrealreaders = 1; > > } > > -- > > 1.8.1.5 > > >