Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756658Ab2HPVzh (ORCPT ); Thu, 16 Aug 2012 17:55:37 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:60707 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755827Ab2HPVz3 (ORCPT ); Thu, 16 Aug 2012 17:55:29 -0400 Date: Thu, 16 Aug 2012 14:55:11 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, pjt@google.com, tglx@linutronix.de, seto.hidetoshi@jp.fujitsu.com Subject: Re: [PATCH RFC] sched: Make migration_call() safe for stop_machine()-free hotplug Message-ID: <20120816215511.GA30518@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120725215126.GA7350@linux.vnet.ibm.com> <1345110832.29668.12.camel@twins> <20120816191710.GF2445@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120816191710.GF2445@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12081621-5930-0000-0000-00000AF33FF3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2550 Lines: 71 On Thu, Aug 16, 2012 at 12:17:10PM -0700, Paul E. McKenney wrote: [ . . . ] > Another attempted patch below. But this time without the brain-dead "using smp_processor_id() in preemptible" bug. Thanx, Paul ------------------------------------------------------------------------ sched: Make migration_call() safe for stop_machine()-free hotplug The CPU_DYING branch of migration_call() relies on the fact that CPU-hotplug offline operations use stop_machine(). This commit therefore attempts to remedy this situation by moving work to the CPU_DEAD notifier when the outgoing CPU is quiescent. This requires a small change to migrate_nr_uninterruptible() to move counts to the current running CPU instead of a randomly selected CPU. Signed-off-by: Paul E. McKenney diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d325c4b..d09c4e0 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5303,12 +5303,12 @@ void idle_task_exit(void) * While a dead CPU has no uninterruptible tasks queued at this point, * it might still have a nonzero ->nr_uninterruptible counter, because * for performance reasons the counter is not stricly tracking tasks to - * their home CPUs. So we just add the counter to another CPU's counter, + * their home CPUs. So we just add the counter to the running CPU's counter, * to keep the global sum constant after CPU-down: */ static void migrate_nr_uninterruptible(struct rq *rq_src) { - struct rq *rq_dest = cpu_rq(cpumask_any(cpu_active_mask)); + struct rq *rq_dest = cpu_rq(smp_processor_id()); rq_dest->nr_uninterruptible += rq_src->nr_uninterruptible; rq_src->nr_uninterruptible = 0; @@ -5613,9 +5613,19 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) migrate_tasks(cpu); BUG_ON(rq->nr_running != 1); /* the migration thread */ raw_spin_unlock_irqrestore(&rq->lock, flags); + break; - migrate_nr_uninterruptible(rq); - calc_global_load_remove(rq); + case CPU_DEAD: + { + struct rq *dest_rq = cpu_rq(smp_processor_id()); + + local_irq_save(flags); + raw_spin_lock(&dest_rq->lock); + migrate_nr_uninterruptible(rq); + calc_global_load_remove(rq); + raw_spin_unlock(&dest_rq->lock); + local_irq_restore(flags); + } break; #endif } -- 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/