From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754226AbbJGO0m (ORCPT ); Wed, 7 Oct 2015 10:26:42 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:51388 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750944AbbJGO0l (ORCPT ); Wed, 7 Oct 2015 10:26:41 -0400 Date: Wed, 7 Oct 2015 16:26:27 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.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 18/18] rcu: Better hotplug handling for synchronize_sched_expedited() Message-ID: <20151007142627.GE3604@twins.programming.kicks-ass.net> References: <20151006162907.GA12020@linux.vnet.ibm.com> <1444148977-14108-1-git-send-email-paulmck@linux.vnet.ibm.com> <1444148977-14108-18-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: <1444148977-14108-18-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 06, 2015 at 09:29:37AM -0700, Paul E. McKenney wrote: > void rcu_sched_qs(void) > { > + unsigned long flags; > + > if (__this_cpu_read(rcu_sched_data.cpu_no_qs.s)) { > trace_rcu_grace_period(TPS("rcu_sched"), > __this_cpu_read(rcu_sched_data.gpnum), > TPS("cpuqs")); > __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false); > + if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) > + return; > + local_irq_save(flags); > if (__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) { > __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false); > rcu_report_exp_rdp(&rcu_sched_state, > this_cpu_ptr(&rcu_sched_data), > true); > } > + local_irq_restore(flags); > } > } *sigh*.. still rare I suppose, but should we look at doing something like this? --- kernel/sched/core.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fe819298c220..3d830c3491c4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3050,7 +3050,6 @@ static void __sched __schedule(void) cpu = smp_processor_id(); rq = cpu_rq(cpu); - rcu_note_context_switch(); prev = rq->curr; schedule_debug(prev); @@ -3058,13 +3057,16 @@ static void __sched __schedule(void) if (sched_feat(HRTICK)) hrtick_clear(rq); + local_irq_disable(); + rcu_note_context_switch(); + /* * Make sure that signal_pending_state()->signal_pending() below * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE) * done by the caller to avoid the race with signal_wake_up(). */ smp_mb__before_spinlock(); - raw_spin_lock_irq(&rq->lock); + raw_spin_lock(&rq->lock); lockdep_pin_lock(&rq->lock); rq->clock_skip_update <<= 1; /* promote REQ to ACT */