Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934306Ab3IDB62 (ORCPT ); Tue, 3 Sep 2013 21:58:28 -0400 Received: from intranet.asianux.com ([58.214.24.6]:42021 "EHLO intranet.asianux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761569Ab3IDB61 (ORCPT ); Tue, 3 Sep 2013 21:58:27 -0400 X-Spam-Score: -100.9 Message-ID: <52269384.4040802@asianux.com> Date: Wed, 04 Sep 2013 09:57:24 +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: paulmck@linux.vnet.ibm.com CC: Chen Gang F T , dipankar@in.ibm.com, "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] kernel/rcutree.c: deem to be lazy if there are no callbacks. References: <5212E7BB.4020602@asianux.com> <20130820041832.GY29406@linux.vnet.ibm.com> <5212F3E5.7080700@asianux.com> <5212F467.8090407@asianux.com> <52145741.7000008@asianux.com> <20130821142301.GX29406@linux.vnet.ibm.com> <52157F21.5080200@asianux.com> <20130825191839.GA22515@linux.vnet.ibm.com> <521ABB9E.1050209@gmail.com> <5225766F.4000907@asianux.com> <20130903175910.GX3871@linux.vnet.ibm.com> In-Reply-To: <20130903175910.GX3871@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2854 Lines: 88 On 09/04/2013 01:59 AM, Paul E. McKenney wrote: > On Tue, Sep 03, 2013 at 01:41:03PM +0800, Chen Gang wrote: >> Hello Maintainers: >> >> Is this issue finished ? >> >> If need additional help from me (e.g. some test things, or others, if >> you have no time, can let me try), please let me know, I should try. > > Ah, sorry, here is the patch. > Thanks. :-) > Thanx, Paul > > ------------------------------------------------------------------------ > > rcu: Micro-optimize rcu_cpu_has_callbacks() > > 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 > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index b1b959d..38596be 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -2756,10 +2756,13 @@ 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; > @@ -3326,8 +3329,8 @@ 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/