From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755056Ab3IYC4i (ORCPT ); Tue, 24 Sep 2013 22:56:38 -0400 Received: from intranet.asianux.com ([58.214.24.6]:24229 "EHLO intranet.asianux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753738Ab3IYC4h (ORCPT ); Tue, 24 Sep 2013 22:56:37 -0400 X-Spam-Score: -100.8 Message-ID: <524250A2.3050502@asianux.com> Date: Wed, 25 Sep 2013 10:55:30 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: "Paul E. McKenney" CC: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, "linux-kernel@vger.kernel.org" Subject: Re: [PATCH tip/core/rcu 08/11] rcu: Micro-optimize rcu_cpu_has_callbacks() References: <20130925012750.GA30601@linux.vnet.ibm.com> <1380072561-31134-1-git-send-email-paulmck@linux.vnet.ibm.com> <1380072561-31134-8-git-send-email-paulmck@linux.vnet.ibm.com> In-Reply-To: <1380072561-31134-8-git-send-email-paulmck@linux.vnet.ibm.com> Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thank you for your whole work, firstly :-). And your suggestion about testing (in our discussion) is also valuable to me. I need start LTP in q4. After referenced your suggestion, my first step for using/learning LTP is not mainly for finding kernel issues, but for testing kernel (to improve my kernel testing efficiency). When I want to find issues by reading code, I will consider about LTP too (I will try to find issues which can be tested by LTP). On 09/25/2013 09:29 AM, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > The for_each_rcu_flavor() loop unconditionally scans all flavors, even > when the first flavor might have some non-lazy callbacks. Once the > loop has seen a non-lazy callback, further passes through the loop > cannot change the state. This is not a huge problem, given that there > can be at most three RCU flavors (RCU-bh, RCU-preempt, and RCU-sched), > but this code is on the path to idle, so speeding it up even a small > amount would have some benefit. > > This commit therefore does two things: > > 1. Rearranges the order of the list of RCU flavors in order to > place the most active flavor first in the list. The most active > RCU flavor is RCU-preempt, or, if there is no RCU-preempt, > RCU-sched. > > 2. Reworks the for_each_rcu_flavor() to exit early when the first > non-lazy callback is seen, or, in the case where the caller > does not care about non-lazy callbacks (RCU_FAST_NO_HZ=n), > when the first callback is seen. > > Reported-by: Chen Gang > Signed-off-by: Paul E. McKenney > --- > kernel/rcutree.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index e6f2e8f..49464ad 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -2727,10 +2727,13 @@ static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy) > > for_each_rcu_flavor(rsp) { > rdp = per_cpu_ptr(rsp->rda, cpu); > - if (rdp->qlen != rdp->qlen_lazy) > + if (!rdp->nxtlist) > + continue; > + hc = true; > + if (rdp->qlen != rdp->qlen_lazy || !all_lazy) { > al = false; > - if (rdp->nxtlist) > - hc = true; > + break; > + } > } > if (all_lazy) > *all_lazy = al; > @@ -3297,8 +3300,8 @@ void __init rcu_init(void) > > rcu_bootup_announce(); > rcu_init_geometry(); > - rcu_init_one(&rcu_sched_state, &rcu_sched_data); > rcu_init_one(&rcu_bh_state, &rcu_bh_data); > + rcu_init_one(&rcu_sched_state, &rcu_sched_data); > __rcu_init_preempt(); > open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); > > -- Chen Gang -- Chen Gang