From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965088AbbEMBDU (ORCPT ); Tue, 12 May 2015 21:03:20 -0400 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:43494 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964800AbbEMBDT (ORCPT ); Tue, 12 May 2015 21:03:19 -0400 Date: Tue, 12 May 2015 18:03:13 -0700 From: josh@joshtriplett.org To: "Paul E. McKenney" 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: <20150513010313.GF14292@cloud> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1431471493-5431-4-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. However, could you please document this in the module parameter documentation? > 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 >