From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753044Ab2GZV01 (ORCPT ); Thu, 26 Jul 2012 17:26:27 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:41537 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752142Ab2GZVUd (ORCPT ); Thu, 26 Jul 2012 17:20:33 -0400 Date: Thu, 26 Jul 2012 14:19:27 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, sbw@mit.edu, srivatsa.bhat@linux.vnet.ibm.com, rusty@rustcorp.com.au, vincent.guittot@linaro.org, amit.kucheria@linaro.org Subject: [PATCH RFC] cpu: No more __stop_machine() in _cpu_down() Message-ID: <20120726211927.GA26016@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12072621-2356-0000-0000-000000B8C1B9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The _cpu_down() function invoked as part of the CPU-hotplug offlining process currently invokes __stop_machine(), which is slow and inflicts substantial real-time latencies on the entire system. This patch substitutes stop_cpus() for __stop_machine() in order to improve both performance and real-time latency. This is currently unsafe, because there are a number of uses of preempt_disable() that are intended to block CPU-hotplug offlining. These will be fixed, but in the meantime, this commit is one way to help locate them. It nevertheless passes light rcutorture/hotplug stress testing. Meaning that we should not be relying on pure testing to find places where people are relying on preemption disabling to block CPUs from going offline. ;-) Not-yet-signed-off-by: Paul E. McKenney diff --git a/kernel/cpu.c b/kernel/cpu.c index a4eb522..47e63a0 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -243,13 +243,18 @@ static int __ref take_cpu_down(void *_param) { struct take_cpu_down_param *param = _param; int err; + unsigned long flags; /* Ensure this CPU doesn't handle any more interrupts. */ + local_irq_save(flags); err = __cpu_disable(); - if (err < 0) + if (err < 0) { + local_irq_restore(flags); return err; + } cpu_notify(CPU_DYING | param->mod, param->hcpu); + local_irq_restore(flags); return 0; } @@ -281,7 +286,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) goto out_release; } - err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu)); + err = stop_cpus(cpumask_of(cpu), take_cpu_down, &tcd_param); if (err) { /* CPU didn't die: tell everyone. Can't complain. */ cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);