From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751936AbbCGSI2 (ORCPT ); Sat, 7 Mar 2015 13:08:28 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:38978 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750802AbbCGSI0 (ORCPT ); Sat, 7 Mar 2015 13:08:26 -0500 Date: Sat, 7 Mar 2015 10:08:21 -0800 From: "Paul E. McKenney" To: Alexander Gordeev Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/9] rcu: Cleanup rcu_init_geometry() code and arithmetics Message-ID: <20150307180821.GN5236@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15030718-0017-0000-0000-000009473077 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 07, 2015 at 06:03:38PM +0100, Alexander Gordeev wrote: > This update simplifies rcu_init_geometry() code flow > and makes calculation of the total number of rcu_node > structures more easy to read. > > The update relies on the fact num_rcu_lvl[] is never > accessed beyond rcu_num_lvls index by the rest of the > code. Therefore, there is no need initialize the whole > num_rcu_lvl[]. > > Cc: "Paul E. McKenney" > Signed-off-by: Alexander Gordeev The rest of this series looks promising, but I do have to ask... How have you tested these? The most straightforward approach would be to find a KVM-capable system with at least 16 CPUs and type the following from the top-level directory: sh tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 34 --duration 5 This will do a series of 16 build-boot-test cycles with various configs (including various rcu_node tree shapes), and print a summary of the outcome at the end. For these sorts of changes, I usually also do some user-level testing. Thanx, Paul > --- > kernel/rcu/tree.c | 24 ++++++++++-------------- > 1 file changed, 10 insertions(+), 14 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index fb89630..f9ef1e0 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -3854,7 +3854,6 @@ static void __init rcu_init_geometry(void) > { > ulong d; > int i; > - int j; > int rcu_capacity[MAX_RCU_LVLS + 1]; > > /* > @@ -3905,24 +3904,21 @@ static void __init rcu_init_geometry(void) > return; > } > > + /* Calculate the number of levels in the tree. */ > + for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) { > + } > + rcu_num_lvls = i; > + > /* Calculate the number of rcu_nodes at each level of the tree. */ > - for (i = 1; i <= MAX_RCU_LVLS; i++) > - if (nr_cpu_ids <= rcu_capacity[i]) { > - for (j = 0; j <= i; j++) { > - int cap = rcu_capacity[i - j]; > - num_rcu_lvl[j] = DIV_ROUND_UP(nr_cpu_ids, cap); > - } > - rcu_num_lvls = i; > - for (j = i + 1; j <= MAX_RCU_LVLS; j++) > - num_rcu_lvl[j] = 0; > - break; > - } > + for (i = 0; i < rcu_num_lvls; i++) { > + int cap = rcu_capacity[rcu_num_lvls - i]; > + num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap); > + } > > /* Calculate the total number of rcu_node structures. */ > rcu_num_nodes = 0; > - for (i = 0; i <= MAX_RCU_LVLS; i++) > + for (i = 0; i < rcu_num_lvls; i++) > rcu_num_nodes += num_rcu_lvl[i]; > - rcu_num_nodes -= nr_cpu_ids; > } > > void __init rcu_init(void) > -- > 1.8.3.1 >