Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756532AbZKCE3F (ORCPT ); Mon, 2 Nov 2009 23:29:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756491AbZKCE3E (ORCPT ); Mon, 2 Nov 2009 23:29:04 -0500 Received: from ozlabs.org ([203.10.76.45]:39516 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756479AbZKCE3D (ORCPT ); Mon, 2 Nov 2009 23:29:03 -0500 To: linux-kernel@vger.kernel.org From: Rusty Russell Message-Id: <200911031459.06857.rusty@rustcorp.com.au> Date: Tue, 3 Nov 2009 14:59:06 +1030 Cc: Andrew Morton , Gautham R Shenoy , Ashok Raj Subject: [PATCH 14/14] cpumask: don't recommend set_cpus_allowed hack in Documentation/cpu-hotplug.txt Cc: Gautham R Shenoy Cc: Ashok Raj MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2218 Lines: 75 Signed-off-by: Rusty Russell Cc: Gautham R Shenoy Cc: Ashok Raj --- Documentation/cpu-hotplug.txt | 49 ++++++++++++++---------------------------- 1 file changed, 17 insertions(+), 32 deletions(-) diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -309,41 +309,26 @@ A: The following are what is required fo Q: I need to ensure that a particular cpu is not removed when there is some work specific to this cpu is in progress. -A: First switch the current thread context to preferred cpu +A: There are two ways. If your code can be run in interrupt context, use + smp_call_function_single(), otherwise use work_on_cpu(). Note that + work_on_cpu() can fail due to out of memory: int my_func_on_cpu(int cpu) { - cpumask_t saved_mask, new_mask = CPU_MASK_NONE; - int curr_cpu, err = 0; - - saved_mask = current->cpus_allowed; - cpu_set(cpu, new_mask); - err = set_cpus_allowed(current, new_mask); - - if (err) - return err; - - /* - * If we got scheduled out just after the return from - * set_cpus_allowed() before running the work, this ensures - * we stay locked. - */ - curr_cpu = get_cpu(); - - if (curr_cpu != cpu) { - err = -EAGAIN; - goto ret; - } else { - /* - * Do work : But cant sleep, since get_cpu() disables preempt - */ - } - ret: - put_cpu(); - set_cpus_allowed(current, saved_mask); - return err; - } - + int err; + cpu_hotplug_lock(); + if (!cpu_online(cpu)) + err = -EINVAL; + else +#if NEEDS_BLOCKING + err = work_on_cpu(cpu, __my_func_on_cpu, NULL); +#else + smp_call_function_single(cpu, __my_func_on_cpu, &err, + true); +#endif + cpu_hotplug_unlock(); + return err; + } Q: How do we determine how many CPUs are available for hotplug. A: There is no clear spec defined way from ACPI that can give us that -- 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/