diff options
| -rw-r--r-- | include/linux/cpu.h | 2 | ||||
| -rw-r--r-- | kernel/workqueue.c | 293 |
2 files changed, 279 insertions, 16 deletions
diff --git a/include/linux/cpu.h b/include/linux/cpu.h index de6b1722cdc..4823af64e9d 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -71,6 +71,8 @@ enum { /* migration should happen before other stuff but after perf */ CPU_PRI_PERF = 20, CPU_PRI_MIGRATION = 10, + /* prepare workqueues for other notifiers */ + CPU_PRI_WORKQUEUE = 5, }; #ifdef CONFIG_SMP diff --git a/kernel/workqueue.c b/kernel/workqueue.c index d64913aa486..f57855f718d 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -36,14 +36,27 @@ #include <linux/idr.h> enum { + /* global_cwq flags */ + GCWQ_FREEZING = 1 << 3, /* freeze in progress */ + /* worker flags */ WORKER_STARTED = 1 << 0, /* started */ WORKER_DIE = 1 << 1, /* die die die */ WORKER_IDLE = 1 << 2, /* is idle */ + WORKER_ROGUE = 1 << 4, /* not bound to any cpu */ + + /* gcwq->trustee_state */ + TRUSTEE_START = 0, /* start */ + TRUSTEE_IN_CHARGE = 1, /* trustee in charge of gcwq */ + TRUSTEE_BUTCHER = 2, /* butcher workers */ + TRUSTEE_RELEASE = 3, /* release workers */ + TRUSTEE_DONE = 4, /* trustee is done */ BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */ BUSY_WORKER_HASH_SIZE = 1 << BUSY_WORKER_HASH_ORDER, BUSY_WORKER_HASH_MASK = BUSY_WORKER_HASH_SIZE - 1, + + TRUSTEE_COOLDOWN = HZ / 10, /* for trustee draining */ }; /* @@ -83,6 +96,7 @@ struct worker { struct global_cwq { spinlock_t lock; /* the gcwq lock */ unsigned int cpu; /* I: the associated cpu */ + unsigned int flags; /* L: GCWQ_* flags */ int nr_workers; /* L: total number of workers */ int nr_idle; /* L: currently idle ones */ @@ -93,6 +107,10 @@ struct global_cwq { /* L: hash of busy workers */ struct ida worker_ida; /* L: for worker IDs */ + + struct task_struct *trustee; /* L: for gcwq shutdown */ + unsigned int trustee_state; /* L: trustee state */ + wait_queue_head_t trustee_wait; /* trustee wait */ } ____cacheline_aligned_in_smp; /* @@ -148,6 +166,10 @@ struct workqueue_struct { #endif }; +#define for_each_busy_worker(worker, i, pos, gcwq) \ + for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++) \ + hlist_for_each_entry(worker, pos, &gcwq->busy_hash[i], hentry) + #ifdef CONFIG_DEBUG_OBJECTS_WORK static struct debug_obj_descr work_debug_descr; @@ -546,6 +568,9 @@ static void worker_enter_idle(struct worker *worker) /* idle_list is LIFO */ list_add(&worker->entry, &gcwq->idle_list); + + if (unlikely(worker->flags & WORKER_ROGUE)) + wake_up_all(&gcwq->trustee_wait); } /** @@ -622,8 +647,15 @@ static struct worker *create_worker(struct cpu_workqueue_struct *cwq, bool bind) if (IS_ERR(worker->task)) goto fail; + /* + * A rogue worker will become a regular one if CPU comes + * online later on. Make sure every worker has + * PF_THREAD_BOUND set. + */ if (bind) kthread_bind(worker->task, gcwq->cpu); + else + worker->task->flags |= PF_THREAD_BOUND; return worker; fail: @@ -882,10 +914,6 @@ static int worker_thread(void *__worker) struct cpu_workqueue_struct *cwq = worker->cwq; woke_up: - if (unlikely(!cpumask_equal(&worker->task->cpus_allowed, - get_cpu_mask(gcwq->cpu)))) - set_cpus_allowed_ptr(worker->task, get_cpu_mask(gcwq->cpu)); - spin_lock_irq(&gcwq->lock); /* DIE can be set only while we're idle, checking here is enough */ @@ -895,7 +923,7 @@ woke_up: } worker_leave_idle(worker); - +recheck: /* * ->scheduled list can only be filled while a worker is * preparing to process a work or actually processing it. @@ -908,6 +936,22 @@ woke_up: list_first_entry(&cwq->worklist, struct work_struct, entry); + /* + * The following is a rather inefficient way to close + * race window against cpu hotplug operations. Will + * be replaced soon. + */ + if (unlikely(!(worker->flags & WORKER_ROGUE) && + !cpumask_equal(&worker->task->cpus_allowed, + get_cpu_mask(gcwq->cpu)))) { + spin_unlock_irq(&gcwq->lock); + set_cpus_allowed_ptr(worker->task, + get_cpu_mask(gcwq->cpu)); + cpu_relax(); + spin_lock_irq(&gcwq->lock); + goto recheck; + } + if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) { /* optimization path, not strictly necessary */ process_one_work(worker, work); @@ -1812,29 +1856,237 @@ void destroy_workqueue(struct workqueue_struct *wq) } EXPORT_SYMBOL_GPL(destroy_workqueue); +/* + * CPU hotplug. + * + * CPU hotplug is implemented by allowing cwqs to be detached from + * CPU, running with unbound workers and allowing them to be + * reattached later if the cpu comes back online. A separate thread + * is created to govern cwqs in such state and is called the trustee. + * + * Trustee states and their descriptions. + * + * START Command state used on startup. On CPU_DOWN_PREPARE, a + * new trustee is started with this state. + * + * IN_CHARGE Once started, trustee will enter this state after + * making all existing workers rogue. DOWN_PREPARE waits + * for trustee to enter this state. After reaching + * IN_CHARGE, trustee tries to execute the pending + * worklist until it's empty and the state is set to + * BUTCHER, or the state is set to RELEASE. + * + * BUTCHER Command state which is set by the cpu callback after + * the cpu has went down. Once this state is set trustee + * knows that there will be no new works on the worklist + * and once the worklist is empty it can proceed to + * killing idle workers. + * + * RELEASE Command state which is set by the cpu callback if the + * cpu down has been canceled or it has come online + * again. After recognizing this state, trustee stops + * trying to drain or butcher and transits to DONE. + * + * DONE Trustee will enter this state after BUTCHER or RELEASE + * is complete. + * + * trustee CPU draining + * took over down complete + * START -----------> IN_CHARGE -----------> BUTCHER -----------> DONE + * | | ^ + * | CPU is back online v return workers | + * ----------------> RELEASE -------------- + */ + +/** + * trustee_wait_event_timeout - timed event wait for trustee + * @cond: condition to wait for + * @timeout: timeout in jiffies + * + * wait_event_timeout() for trustee to use. Handles locking and + * checks for RELEASE request. + * + * CONTEXT: + * spin_lock_irq(gcwq->lock) which may be released and regrabbed + * multiple times. To be used by trustee. + * + * RETURNS: + * Positive indicating left time if @cond is satisfied, 0 if timed + * out, -1 if canceled. + */ +#define trustee_wait_event_timeout(cond, timeout) ({ \ + long __ret = (timeout); \ + while (!((cond) || (gcwq->trustee_state == TRUSTEE_RELEASE)) && \ + __ret) { \ + spin_unlock_irq(&gcwq->lock); \ + __wait_event_timeout(gcwq->trustee_wait, (cond) || \ + (gcwq->trustee_state == TRUSTEE_RELEASE), \ + __ret); \ + spin_lock_irq(&gcwq->lock); \ + } \ + gcwq->trustee_state == TRUSTEE_RELEASE ? -1 : (__ret); \ +}) + +/** + * trustee_wait_event - event wait for trustee + * @cond: condition to wait for + * + * wait_event() for trustee to use. Automatically handles locking and + * checks for CANCEL request. + * + * CONTEXT: + * spin_lock_irq(gcwq->lock) which may be released and regrabbed + * multiple times. To be used by trustee. + * + * RETURNS: + * 0 if @cond is satisfied, -1 if canceled. + */ +#define trustee_wait_event(cond) ({ \ + long __ret1; \ + __ret1 = trustee_wait_event_timeout(cond, MAX_SCHEDULE_TIMEOUT);\ + __ret1 < 0 ? -1 : 0; \ +}) + +static int __cpuinit trustee_thread(void *__gcwq) +{ + struct global_cwq *gcwq = __gcwq; + struct worker *worker; + struct hlist_node *pos; + int i; + + BUG_ON(gcwq->cpu != smp_processor_id()); + + spin_lock_irq(&gcwq->lock); + /* + * Make all multithread workers rogue. Trustee must be bound + * to the target cpu and can't be cancelled. + */ + BUG_ON(gcwq->cpu != smp_processor_id()); + + list_for_each_entry(worker, &gcwq->idle_list, entry) + if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD)) + worker->flags |= WORKER_ROGUE; + + for_each_busy_worker(worker, i, pos, gcwq) + if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD)) + worker->flags |= WORKER_ROGUE; + + /* + * We're now in charge. Notify and proceed to drain. We need + * to keep the gcwq running during the whole CPU down + * procedure as other cpu hotunplug callbacks may need to + * flush currently running tasks. + */ + gcwq->trustee_state = TRUSTEE_IN_CHARGE; + wake_up_all(&gcwq->trustee_wait); + + /* + * The original cpu is in the process of dying and may go away + * anytime now. When that happens, we and all workers would + * be migrated to other cpus. Try draining any left work. + * Note that if the gcwq is frozen, there may be frozen works + * in freezeable cwqs. Don't declare completion while frozen. + */ + while (gcwq->nr_workers != gcwq->nr_idle || + gcwq->flags & GCWQ_FREEZING || + gcwq->trustee_state == TRUSTEE_IN_CHARGE) { + /* give a breather */ + if (trustee_wait_event_timeout(false, TRUSTEE_COOLDOWN) < 0) + break; + } + + /* notify completion */ + gcwq->trustee = NULL; + gcwq->trustee_state = TRUSTEE_DONE; + wake_up_all(&gcwq->trustee_wait); + spin_unlock_irq(&gcwq->lock); + return 0; +} + +/** + * wait_trustee_state - wait for trustee to enter the specified state + * @gcwq: gcwq the trustee of interest belongs to + * @state: target state to wait for + * + * Wait for the trustee to reach @state. DONE is already matched. + * + * CONTEXT: + * spin_lock_irq(gcwq->lock) which may be released and regrabbed + * multiple times. To be used by cpu_callback. + */ +static void __cpuinit wait_trustee_state(struct global_cwq *gcwq, int state) +{ + if (!(gcwq->trustee_state == state || + gcwq->trustee_state == TRUSTEE_DONE)) { + spin_unlock_irq(&gcwq->lock); + __wait_event(gcwq->trustee_wait, + gcwq->trustee_state == state || + gcwq->trustee_state == TRUSTEE_DONE); + spin_lock_irq(&gcwq->lock); + } +} + static int __devinit workqueue_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) { unsigned int cpu = (unsigned long)hcpu; - struct cpu_workqueue_struct *cwq; - struct workqueue_struct *wq; + struct global_cwq *gcwq = get_gcwq(cpu); + struct task_struct *new_trustee = NULL; + struct worker *worker; + struct hlist_node *pos; + unsigned long flags; + int i; action &= ~CPU_TASKS_FROZEN; - list_for_each_entry(wq, &workqueues, list) { - if (wq->flags & WQ_SINGLE_THREAD) - continue; + switch (action) { + case CPU_DOWN_PREPARE: + new_trustee = kthread_create(trustee_thread, gcwq, + "workqueue_trustee/%d\n", cpu); + if (IS_ERR(new_trustee)) + return notifier_from_errno(PTR_ERR(new_trustee)); + kthread_bind(new_trustee, cpu); + } - cwq = get_cwq(cpu, wq); + /* some are called w/ irq disabled, don't disturb irq status */ + spin_lock_irqsave(&gcwq->lock, flags); - switch (action) { - case CPU_POST_DEAD: - flush_workqueue(wq); - break; + switch (action) { + case CPU_DOWN_PREPARE: + /* initialize trustee and tell it to acquire the gcwq */ + BUG_ON(gcwq->trustee || gcwq->trustee_state != TRUSTEE_DONE); + gcwq->trustee = new_trustee; + gcwq->trustee_state = TRUSTEE_START; + wake_up_process(gcwq->trustee); + wait_trustee_state(gcwq, TRUSTEE_IN_CHARGE); + break; + + case CPU_POST_DEAD: + gcwq->trustee_state = TRUSTEE_BUTCHER; + break; + + case CPU_DOWN_FAILED: + case CPU_ONLINE: + if (gcwq->trustee_state != TRUSTEE_DONE) { + gcwq->trustee_state = TRUSTEE_RELEASE; + wake_up_process(gcwq->trustee); + wait_trustee_state(gcwq, TRUSTEE_DONE); } + + /* clear ROGUE from all multithread workers */ + list_for_each_entry(worker, &gcwq->idle_list, entry) + if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD)) + worker->flags &= ~WORKER_ROGUE; + + for_each_busy_worker(worker, i, pos, gcwq) + if (!(worker->cwq->wq->flags & WQ_SINGLE_THREAD)) + worker->flags &= ~WORKER_ROGUE; + break; } + spin_unlock_irqrestore(&gcwq->lock, flags); + return notifier_from_errno(0); } @@ -1912,6 +2164,9 @@ void freeze_workqueues_begin(void) spin_lock_irq(&gcwq->lock); + BUG_ON(gcwq->flags & GCWQ_FREEZING); + gcwq->flags |= GCWQ_FREEZING; + list_for_each_entry(wq, &workqueues, list) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); @@ -1995,6 +2250,9 @@ void thaw_workqueues(void) spin_lock_irq(&gcwq->lock); + BUG_ON(!(gcwq->flags & GCWQ_FREEZING)); + gcwq->flags &= ~GCWQ_FREEZING; + list_for_each_entry(wq, &workqueues, list) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); @@ -2026,7 +2284,7 @@ void __init init_workqueues(void) int i; singlethread_cpu = cpumask_first(cpu_possible_mask); - hotcpu_notifier(workqueue_cpu_callback, 0); + hotcpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE); /* initialize gcwqs */ for_each_possible_cpu(cpu) { @@ -2040,6 +2298,9 @@ void __init init_workqueues(void) INIT_HLIST_HEAD(&gcwq->busy_hash[i]); ida_init(&gcwq->worker_ida); + + gcwq->trustee_state = TRUSTEE_DONE; + init_waitqueue_head(&gcwq->trustee_wait); } keventd_wq = create_workqueue("events"); |