From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754771Ab2HaSvv (ORCPT ); Fri, 31 Aug 2012 14:51:51 -0400 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:51561 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754275Ab2HaSvu (ORCPT ); Fri, 31 Aug 2012 14:51:50 -0400 X-Originating-IP: 217.70.178.146 X-Originating-IP: 173.246.103.110 Date: Fri, 31 Aug 2012 11:51:41 -0700 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Subject: Re: [PATCH tip/core/rcu 14/15] time: RCU permitted to stop idle entry via softirq Message-ID: <20120831185141.GN4259@jtriplet-mobl1> References: <20120830185607.GA32148@linux.vnet.ibm.com> <1346352988-32444-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346352988-32444-14-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: <1346352988-32444-14-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 30, 2012 at 11:56:27AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > The can_stop_idle_tick() function complains if a softirq vector is > raised too late in the idle-entry process, presumably in order to > prevent dangling softirq invocations from being delayed across the > full idle period, which might be indefinitely long -- and if softirq > was asserted any later than the call to this function, such a delay > might well happen. > > However, RCU needs to be able to use softirq to stop idle entry in > order to be able to drain RCU callbacks from the current CPU, which in > turn enables faster entry into dyntick-idle mode, which in turn reduces > power consumption. Because RCU takes this action at a well-defined > point in the idle-entry path, it is safe for RCU to take this approach. > > This commit therefore silences the error message that is sometimes > produced when the going-idle CPU suddenly finds that it has an RCU_SOFTIRQ > to process. The error message will continue to be issued for other > softirq vectors. > > Reported-by: Sedat Dilek > Signed-off-by: Paul E. McKenney > Signed-off-by: Paul E. McKenney > Tested-by: Sedat Dilek Reviewed-by: Josh Triplett > --- > include/linux/interrupt.h | 2 ++ > kernel/time/tick-sched.c | 3 ++- > 2 files changed, 4 insertions(+), 1 deletions(-) > > diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h > index c5f856a..5e4e617 100644 > --- a/include/linux/interrupt.h > +++ b/include/linux/interrupt.h > @@ -430,6 +430,8 @@ enum > NR_SOFTIRQS > }; > > +#define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ)) > + > /* map softirq index to softirq name. update 'softirq_to_name' in > * kernel/softirq.c when adding a new softirq. > */ > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 024540f..4b1785a 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -436,7 +436,8 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) > if (unlikely(local_softirq_pending() && cpu_online(cpu))) { > static int ratelimit; > > - if (ratelimit < 10) { > + if (ratelimit < 10 && > + (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { > printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", > (unsigned int) local_softirq_pending()); > ratelimit++; > -- > 1.7.8 >