From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932556AbaJ2LAB (ORCPT ); Wed, 29 Oct 2014 07:00:01 -0400 Received: from casper.infradead.org ([85.118.1.10]:41931 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932255AbaJ2LAA (ORCPT ); Wed, 29 Oct 2014 07:00:00 -0400 Date: Wed, 29 Oct 2014 11:59:54 +0100 From: Peter Zijlstra 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, josh@joshtriplett.org, tglx@linutronix.de, 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 3/7] rcu: Avoid IPIing idle CPUs from synchronize_sched_expedited() Message-ID: <20141029105954.GZ3337@twins.programming.kicks-ass.net> References: <20141028222224.GA28263@linux.vnet.ibm.com> <1414534982-29203-1-git-send-email-paulmck@linux.vnet.ibm.com> <1414534982-29203-3-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: <1414534982-29203-3-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 28, 2014 at 03:22:58PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > Currently, synchronize_sched_expedited() sends IPIs to all online CPUs, > even those that are idle or executing in nohz_full= userspace. Because > idle CPUs and nohz_full= userspace CPUs are in extended quiescent states, > there is no need to IPI them in the first place. This commit therefore > avoids IPIing CPUs that are already in extended quiescent states. > > Signed-off-by: Paul E. McKenney > --- > kernel/rcu/tree.c | 27 ++++++++++++++++++++++++++- > 1 file changed, 26 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 7f73c5edf8cf..9e3c20f117cd 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2950,6 +2950,9 @@ static int synchronize_sched_expedited_cpu_stop(void *data) > */ > void synchronize_sched_expedited(void) > { > + cpumask_var_t cm; > + bool cma = false; > + int cpu; > long firstsnap, s, snap; > int trycount = 0; > struct rcu_state *rsp = &rcu_sched_state; > @@ -2984,11 +2987,26 @@ void synchronize_sched_expedited(void) > } > WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id())); > > + /* Offline CPUs, idle CPUs, and any CPU we run on are quiescent. */ > + cma = zalloc_cpumask_var(&cm, GFP_KERNEL); > + if (cma) { > + cpumask_copy(cm, cpu_online_mask); > + cpumask_clear_cpu(raw_smp_processor_id(), cm); > + for_each_cpu(cpu, cm) { > + struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); > + > + if (!(atomic_add_return(0, &rdtp->dynticks) & 0x1)) > + cpumask_clear_cpu(cpu, cm); > + } > + if (cpumask_weight(cm) == 0) > + goto all_cpus_idle; > + } Is there a reason not to use on_each_cpu_cond()?