Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932547AbXAQRD1 (ORCPT ); Wed, 17 Jan 2007 12:03:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932549AbXAQRD0 (ORCPT ); Wed, 17 Jan 2007 12:03:26 -0500 Received: from mail.screens.ru ([213.234.233.54]:35915 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932547AbXAQRD0 (ORCPT ); Wed, 17 Jan 2007 12:03:26 -0500 Date: Wed, 17 Jan 2007 20:01:36 +0300 From: Oleg Nesterov To: Srivatsa Vaddagiri Cc: Andrew Morton , David Howells , Christoph Hellwig , Ingo Molnar , Linus Torvalds , linux-kernel@vger.kernel.org, Gautham shenoy , "Pallipadi, Venkatesh" Subject: Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist Message-ID: <20070117170136.GA2924@tv-sign.ru> References: <20070114235410.GA6165@tv-sign.ru> <20070115043304.GA16435@in.ibm.com> <20070115125401.GA134@tv-sign.ru> <20070115161810.GB16435@in.ibm.com> <20070115165516.GA254@tv-sign.ru> <20070116052606.GA995@in.ibm.com> <20070116132725.GA81@tv-sign.ru> <20070117061705.GB2803@in.ibm.com> <20070117154716.GA104@tv-sign.ru> <20070117161207.GE26211@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070117161207.GE26211@in.ibm.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5932 Lines: 262 On 01/17, Srivatsa Vaddagiri wrote: > > On Wed, Jan 17, 2007 at 06:47:16PM +0300, Oleg Nesterov wrote: > > > What do you mean by "currently" executing work? worker thread executing > > > some work on the cpu? That is not possible, because all threads are > > > frozen at this point. There cant be any ongoing flush_workxxx() as well > > > because of this, which should avoid breaking flush_workxxx() .. > > > > work->func() sleeps/freezed. > > Didnt Andrew call that (work->func calling try_to_freeze) madness? > > http://lkml.org/lkml/2007/01/07/166 This means we should move try_to_freeze() to run_workqueue() or we should forbid auto-requeued works. I don't have a time to do anything till weekend, but please see a "final" version below. - Do you see any bugs? - Do you agree it is better than we have now? If/when we use freezer/lock_cpu_hotplug() we probably can simplfy things further. Note: schedule_on_each_cpu() remains broken. Oleg. struct cpu_workqueue_srtuct { ... int should_stop; ... }; static cpumask_t cpu_populated_map __read_mostly; //also used in flush_work... static int embryonic_cpu __read_mostly = -1; /* * NOTE: the caller must not touch *cwq if this func returns true */ static inline int cwq_should_stop(struct cpu_workqueue_struct *cwq) { int should_stop = cwq->should_stop; if (unlikely(should_stop)) { spin_lock_irq(&cwq->lock); should_stop = cwq->should_stop && list_empty(&cwq->worklist); if (should_stop) cwq->thread = NULL; spin_unlock_irq(&cwq->lock); } return should_stop; } static int worker_thread(void *cwq) { ... while (!cwq_should_stop(cwq)) { if (cwq->wq->freezeable) try_to_freeze(); prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE); if (!cwq->should_stop && list_empty(&cwq->worklist)) schedule(); finish_wait(&cwq->more_work, &wait); run_workqueue(cwq); } return 0; } static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu) { struct task_struct *p; spin_lock_irq(&cwq->lock); cwq->should_stop = 0; p = cwq->thread; spin_unlock_irq(&cwq->lock); if (!p) { struct workqueue_struct *wq = cwq->wq; const char *fmt = is_single_threaded(wq) ? "%s" : "%s/%d"; p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu); /* * Nobody can add the work_struct to this cwq, * if (caller is __create_workqueue) * nobody should see this wq * else // caller is CPU_UP_PREPARE * cpu is not on cpu_online_map * so we can abort safely. */ if (IS_ERR(p)) return PTR_ERR(p); if (!is_single_threaded(wq)) kthread_bind(p, cpu); /* * Cancels affinity if the caller is CPU_UP_PREPARE. * Needs a cleanup, but OK. */ wake_up_process(p); cwq->thread = p; } return 0; } struct workqueue_struct *__create_workqueue(const char *name, int singlethread, int freezeable) { struct workqueue_struct *wq; struct cpu_workqueue_struct *cwq; int err = 0, cpu; wq = kzalloc(sizeof(*wq), GFP_KERNEL); if (!wq) return NULL; wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct); if (!wq->cpu_wq) { kfree(wq); return NULL; } wq->name = name; wq->freezeable = freezeable; if (singlethread) { INIT_LIST_HEAD(&wq->list); cwq = init_cpu_workqueue(wq, singlethread_cpu); err = create_workqueue_thread(cwq, singlethread_cpu); } else { mutex_lock(&workqueue_mutex); list_add(&wq->list, &workqueues); for_each_possible_cpu(cpu) { cwq = init_cpu_workqueue(wq, cpu); if (err || !(cpu_online(cpu) || cpu == embryonic_cpu)) continue; err = create_workqueue_thread(cwq, cpu); } mutex_unlock(&workqueue_mutex); } if (err) { destroy_workqueue(wq); wq = NULL; } return wq; } static void cleanup_workqueue_thread(struct workqueue_struct *wq, int cpu) { struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu); struct wq_barrier barr; int alive = 0; spin_lock_irq(&cwq->lock); if (cwq->thread != NULL) { insert_wq_barrier(cwq, &barr, 1); cwq->should_stop = 1; alive = 1; } spin_unlock_irq(&cwq->lock); if (alive) { wait_for_completion(&barr.done); while (unlikely(cwq->thread != NULL)) cpu_relax(); /* * Wait until cwq->thread unlocks cwq->lock, * it won't touch *cwq after that. */ smp_rmb(); spin_unlock_wait(&cwq->lock); } } void destroy_workqueue(struct workqueue_struct *wq) { if (is_single_threaded(wq)) cleanup_workqueue_thread(wq, singlethread_cpu); else { int cpu; mutex_lock(&workqueue_mutex); list_del(&wq->list); mutex_unlock(&workqueue_mutex); for_each_cpu_mask(cpu, cpu_populated_map) cleanup_workqueue_thread(wq, cpu); } free_percpu(wq->cpu_wq); kfree(wq); } static int __devinit workqueue_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) { struct workqueue_struct *wq; struct cpu_workqueue_struct *cwq; unsigned int cpu = (unsigned long)hcpu; int ret = NOTIFY_OK; mutex_lock(&workqueue_mutex); embryonic_cpu = -1; if (action == CPU_UP_PREPARE) { cpu_set(cpu, cpu_populated_map); embryonic_cpu = cpu; } list_for_each_entry(wq, &workqueues, list) { cwq = per_cpu_ptr(wq->cpu_wq, cpu); switch (action) { case CPU_UP_PREPARE: if (create_workqueue_thread(cwq, cpu)) ret = NOTIFY_BAD; break; case CPU_ONLINE: set_cpus_allowed(cwq->thread, cpumask_of_cpu(cpu)); break; case CPU_UP_CANCELED: case CPU_DEAD: cwq->should_stop = 1; wake_up(&cwq->more_work); break; } if (ret != NOTIFY_OK) { printk(KERN_ERR "workqueue for %i failed\n", cpu); break; } } mutex_unlock(&workqueue_mutex); return ret; } void init_workqueues(void) { ... cpu_populated_map = cpu_online_map; ... } - 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/