Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758927AbYBPRTy (ORCPT ); Sat, 16 Feb 2008 12:19:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757340AbYBPRTY (ORCPT ); Sat, 16 Feb 2008 12:19:24 -0500 Received: from x346.tv-sign.ru ([89.108.83.215]:33384 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756503AbYBPRTW (ORCPT ); Sat, 16 Feb 2008 12:19:22 -0500 Date: Sat, 16 Feb 2008 20:22:54 +0300 From: Oleg Nesterov To: Andrew Morton Cc: Dipankar Sarma , Gautham R Shenoy , Ingo Molnar , Srivatsa Vaddagiri , linux-kernel@vger.kernel.org Subject: [PATCH] simplify cpu_hotplug_begin()/put_online_cpus() Message-ID: <20080216172254.GA18521@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2786 Lines: 85 cpu_hotplug_begin() must be always called under cpu_add_remove_lock, this means that only one process can be cpu_hotplug.active_writer. So we don't need the cpu_hotplug.writer_queue, we can wake up the ->active_writer directly. Also, fix the comment. Signed-off-by: Oleg Nesterov --- 25/kernel/cpu.c~1_CPU_HP_LOCK 2008-02-15 16:59:17.000000000 +0300 +++ 25/kernel/cpu.c 2008-02-16 18:36:37.000000000 +0300 @@ -33,17 +33,13 @@ static struct { * an ongoing cpu hotplug operation. */ int refcount; - wait_queue_head_t writer_queue; } cpu_hotplug; -#define writer_exists() (cpu_hotplug.active_writer != NULL) - void __init cpu_hotplug_init(void) { cpu_hotplug.active_writer = NULL; mutex_init(&cpu_hotplug.lock); cpu_hotplug.refcount = 0; - init_waitqueue_head(&cpu_hotplug.writer_queue); } #ifdef CONFIG_HOTPLUG_CPU @@ -65,11 +61,8 @@ void put_online_cpus(void) if (cpu_hotplug.active_writer == current) return; mutex_lock(&cpu_hotplug.lock); - cpu_hotplug.refcount--; - - if (unlikely(writer_exists()) && !cpu_hotplug.refcount) - wake_up(&cpu_hotplug.writer_queue); - + if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) + wake_up_process(cpu_hotplug.active_writer); mutex_unlock(&cpu_hotplug.lock); } @@ -98,8 +91,8 @@ void cpu_maps_update_done(void) * Note that during a cpu-hotplug operation, the new readers, if any, * will be blocked by the cpu_hotplug.lock * - * Since cpu_maps_update_begin is always called after invoking - * cpu_maps_update_begin, we can be sure that only one writer is active. + * Since cpu_hotplug_begin() is always called after invoking + * cpu_maps_update_begin(), we can be sure that only one writer is active. * * Note that theoretically, there is a possibility of a livelock: * - Refcount goes to zero, last reader wakes up the sleeping @@ -115,19 +108,16 @@ void cpu_maps_update_done(void) */ static void cpu_hotplug_begin(void) { - DECLARE_WAITQUEUE(wait, current); - - mutex_lock(&cpu_hotplug.lock); - cpu_hotplug.active_writer = current; - add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait); - while (cpu_hotplug.refcount) { - set_current_state(TASK_UNINTERRUPTIBLE); + + for (;;) { + mutex_lock(&cpu_hotplug.lock); + if (likely(!cpu_hotplug.refcount)) + break; + __set_current_state(TASK_UNINTERRUPTIBLE); mutex_unlock(&cpu_hotplug.lock); schedule(); - mutex_lock(&cpu_hotplug.lock); } - remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait); } static void cpu_hotplug_done(void) -- 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/