From f34217977d717385a3e9fd7018ac39fade3964c0 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 2 Jul 2010 10:03:51 +0200 Subject: [PATCH] workqueue: implement unbound workqueue This patch implements unbound workqueue which can be specified with WQ_UNBOUND flag on creation. An unbound workqueue has the following properties. * It uses a dedicated gcwq with a pseudo CPU number WORK_CPU_UNBOUND. This gcwq is always online and disassociated. * Workers are not bound to any CPU and not concurrency managed. Works are dispatched to workers as soon as possible and the only applied limitation is @max_active. IOW, all unbound workqeueues are implicitly high priority. Unbound workqueues can be used as simple execution context provider. Contexts unbound to any cpu are served as soon as possible. Signed-off-by: Tejun Heo Cc: Arjan van de Ven Cc: David Howells --- include/linux/workqueue.h | 15 ++- kernel/workqueue.c | 218 +++++++++++++++++++++++++++----------- 2 files changed, 173 insertions(+), 60 deletions(-) diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index 139069a6286..67ce734747f 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -51,7 +51,8 @@ enum { WORK_NO_COLOR = WORK_NR_COLORS, /* special cpu IDs */ - WORK_CPU_NONE = NR_CPUS, + WORK_CPU_UNBOUND = NR_CPUS, + WORK_CPU_NONE = NR_CPUS + 1, WORK_CPU_LAST = WORK_CPU_NONE, /* @@ -237,11 +238,17 @@ enum { WQ_RESCUER = 1 << 3, /* has an rescue worker */ WQ_HIGHPRI = 1 << 4, /* high priority */ WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */ + WQ_UNBOUND = 1 << 6, /* not bound to any cpu */ WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */ + WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */ WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2, }; +/* unbound wq's aren't per-cpu, scale max_active according to #cpus */ +#define WQ_UNBOUND_MAX_ACTIVE \ + max_t(int, WQ_MAX_ACTIVE, num_possible_cpus() * WQ_MAX_UNBOUND_PER_CPU) + /* * System-wide workqueues which are always present. * @@ -256,10 +263,16 @@ enum { * system_nrt_wq is non-reentrant and guarantees that any given work * item is never executed in parallel by multiple CPUs. Queue * flushing might take relatively long. + * + * system_unbound_wq is unbound workqueue. Workers are not bound to + * any specific CPU, not concurrency managed, and all queued works are + * executed immediately as long as max_active limit is not reached and + * resources are available. */ extern struct workqueue_struct *system_wq; extern struct workqueue_struct *system_long_wq; extern struct workqueue_struct *system_nrt_wq; +extern struct workqueue_struct *system_unbound_wq; extern struct workqueue_struct * __alloc_workqueue_key(const char *name, unsigned int flags, int max_active, diff --git a/kernel/workqueue.c b/kernel/workqueue.c index a105ddf55f7..4608563cdd6 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -53,9 +53,10 @@ enum { WORKER_ROGUE = 1 << 4, /* not bound to any cpu */ WORKER_REBIND = 1 << 5, /* mom is home, come back */ WORKER_CPU_INTENSIVE = 1 << 6, /* cpu intensive */ + WORKER_UNBOUND = 1 << 7, /* worker is unbound */ WORKER_NOT_RUNNING = WORKER_PREP | WORKER_ROGUE | WORKER_REBIND | - WORKER_CPU_INTENSIVE, + WORKER_CPU_INTENSIVE | WORKER_UNBOUND, /* gcwq->trustee_state */ TRUSTEE_START = 0, /* start */ @@ -96,7 +97,7 @@ enum { * X: During normal operation, modification requires gcwq->lock and * should be done only from local cpu. Either disabling preemption * on local cpu or grabbing gcwq->lock is enough for read access. - * While trustee is in charge, it's identical to L. + * If GCWQ_DISASSOCIATED is set, it's identical to L. * * F: wq->flush_mutex protected. * @@ -220,14 +221,52 @@ struct workqueue_struct { struct workqueue_struct *system_wq __read_mostly; struct workqueue_struct *system_long_wq __read_mostly; struct workqueue_struct *system_nrt_wq __read_mostly; +struct workqueue_struct *system_unbound_wq __read_mostly; EXPORT_SYMBOL_GPL(system_wq); EXPORT_SYMBOL_GPL(system_long_wq); EXPORT_SYMBOL_GPL(system_nrt_wq); +EXPORT_SYMBOL_GPL(system_unbound_wq); #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) +static inline int __next_gcwq_cpu(int cpu, const struct cpumask *mask, + unsigned int sw) +{ + if (cpu < nr_cpu_ids) { + if (sw & 1) { + cpu = cpumask_next(cpu, mask); + if (cpu < nr_cpu_ids) + return cpu; + } + if (sw & 2) + return WORK_CPU_UNBOUND; + } + return WORK_CPU_NONE; +} + +static inline int __next_wq_cpu(int cpu, const struct cpumask *mask, + struct workqueue_struct *wq) +{ + return __next_gcwq_cpu(cpu, mask, !(wq->flags & WQ_UNBOUND) ? 1 : 2); +} + +#define for_each_gcwq_cpu(cpu) \ + for ((cpu) = __next_gcwq_cpu(-1, cpu_possible_mask, 3); \ + (cpu) < WORK_CPU_NONE; \ + (cpu) = __next_gcwq_cpu((cpu), cpu_possible_mask, 3)) + +#define for_each_online_gcwq_cpu(cpu) \ + for ((cpu) = __next_gcwq_cpu(-1, cpu_online_mask, 3); \ + (cpu) < WORK_CPU_NONE; \ + (cpu) = __next_gcwq_cpu((cpu), cpu_online_mask, 3)) + +#define for_each_cwq_cpu(cpu, wq) \ + for ((cpu) = __next_wq_cpu(-1, cpu_possible_mask, (wq)); \ + (cpu) < WORK_CPU_NONE; \ + (cpu) = __next_wq_cpu((cpu), cpu_possible_mask, (wq))) + #ifdef CONFIG_DEBUG_OBJECTS_WORK static struct debug_obj_descr work_debug_descr; @@ -351,26 +390,46 @@ static bool workqueue_freezing; /* W: have wqs started freezing? */ static DEFINE_PER_CPU(struct global_cwq, global_cwq); static DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, gcwq_nr_running); +/* + * Global cpu workqueue and nr_running counter for unbound gcwq. The + * gcwq is always online, has GCWQ_DISASSOCIATED set, and all its + * workers have WORKER_UNBOUND set. + */ +static struct global_cwq unbound_global_cwq; +static atomic_t unbound_gcwq_nr_running = ATOMIC_INIT(0); /* always 0 */ + static int worker_thread(void *__worker); static struct global_cwq *get_gcwq(unsigned int cpu) { - return &per_cpu(global_cwq, cpu); + if (cpu != WORK_CPU_UNBOUND) + return &per_cpu(global_cwq, cpu); + else + return &unbound_global_cwq; } static atomic_t *get_gcwq_nr_running(unsigned int cpu) { - return &per_cpu(gcwq_nr_running, cpu); + if (cpu != WORK_CPU_UNBOUND) + return &per_cpu(gcwq_nr_running, cpu); + else + return &unbound_gcwq_nr_running; } static struct cpu_workqueue_struct *get_cwq(unsigned int cpu, struct workqueue_struct *wq) { -#ifndef CONFIG_SMP - return wq->cpu_wq.single; + if (!(wq->flags & WQ_UNBOUND)) { + if (likely(cpu < nr_cpu_ids)) { +#ifdef CONFIG_SMP + return per_cpu_ptr(wq->cpu_wq.pcpu, cpu); #else - return per_cpu_ptr(wq->cpu_wq.pcpu, cpu); + return wq->cpu_wq.single; #endif + } + } else if (likely(cpu == WORK_CPU_UNBOUND)) + return wq->cpu_wq.single; + return NULL; } static unsigned int work_color_to_flags(int color) @@ -453,7 +512,7 @@ static struct global_cwq *get_work_gcwq(struct work_struct *work) if (cpu == WORK_CPU_NONE) return NULL; - BUG_ON(cpu >= nr_cpu_ids); + BUG_ON(cpu >= nr_cpu_ids && cpu != WORK_CPU_UNBOUND); return get_gcwq(cpu); } @@ -869,11 +928,14 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq, debug_work_activate(work); + if (unlikely(cpu == WORK_CPU_UNBOUND)) + cpu = raw_smp_processor_id(); + /* * Determine gcwq to use. SINGLE_CPU is inherently * NON_REENTRANT, so test it first. */ - if (!(wq->flags & WQ_SINGLE_CPU)) { + if (!(wq->flags & (WQ_SINGLE_CPU | WQ_UNBOUND))) { struct global_cwq *last_gcwq; /* @@ -900,7 +962,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq, } } else spin_lock_irqsave(&gcwq->lock, flags); - } else { + } else if (!(wq->flags & WQ_UNBOUND)) { unsigned int req_cpu = cpu; /* @@ -932,6 +994,9 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq, spin_unlock_irqrestore(&gcwq->lock, flags); goto retry; } + } else { + gcwq = get_gcwq(WORK_CPU_UNBOUND); + spin_lock_irqsave(&gcwq->lock, flags); } /* gcwq determined, get cwq and queue */ @@ -1166,7 +1231,8 @@ static bool worker_maybe_bind_and_lock(struct worker *worker) * it races with cpu hotunplug operation. Verify * against GCWQ_DISASSOCIATED. */ - set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu)); + if (!(gcwq->flags & GCWQ_DISASSOCIATED)) + set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu)); spin_lock_irq(&gcwq->lock); if (gcwq->flags & GCWQ_DISASSOCIATED) @@ -1231,8 +1297,9 @@ static struct worker *alloc_worker(void) */ static struct worker *create_worker(struct global_cwq *gcwq, bool bind) { - int id = -1; + bool on_unbound_cpu = gcwq->cpu == WORK_CPU_UNBOUND; struct worker *worker = NULL; + int id = -1; spin_lock_irq(&gcwq->lock); while (ida_get_new(&gcwq->worker_ida, &id)) { @@ -1250,8 +1317,12 @@ static struct worker *create_worker(struct global_cwq *gcwq, bool bind) worker->gcwq = gcwq; worker->id = id; - worker->task = kthread_create(worker_thread, worker, "kworker/%u:%d", - gcwq->cpu, id); + if (!on_unbound_cpu) + worker->task = kthread_create(worker_thread, worker, + "kworker/%u:%d", gcwq->cpu, id); + else + worker->task = kthread_create(worker_thread, worker, + "kworker/u:%d", id); if (IS_ERR(worker->task)) goto fail; @@ -1260,10 +1331,13 @@ static struct worker *create_worker(struct global_cwq *gcwq, bool bind) * online later on. Make sure every worker has * PF_THREAD_BOUND set. */ - if (bind) + if (bind && !on_unbound_cpu) kthread_bind(worker->task, gcwq->cpu); - else + else { worker->task->flags |= PF_THREAD_BOUND; + if (on_unbound_cpu) + worker->flags |= WORKER_UNBOUND; + } return worker; fail: @@ -1358,12 +1432,17 @@ static bool send_mayday(struct work_struct *work) { struct cpu_workqueue_struct *cwq = get_work_cwq(work); struct workqueue_struct *wq = cwq->wq; + unsigned int cpu; if (!(wq->flags & WQ_RESCUER)) return false; /* mayday mayday mayday */ - if (!cpumask_test_and_set_cpu(cwq->gcwq->cpu, wq->mayday_mask)) + cpu = cwq->gcwq->cpu; + /* WORK_CPU_UNBOUND can't be set in cpumask, use cpu 0 instead */ + if (cpu == WORK_CPU_UNBOUND) + cpu = 0; + if (!cpumask_test_and_set_cpu(cpu, wq->mayday_mask)) wake_up_process(wq->rescuer->task); return true; } @@ -1882,6 +1961,7 @@ static int rescuer_thread(void *__wq) struct workqueue_struct *wq = __wq; struct worker *rescuer = wq->rescuer; struct list_head *scheduled = &rescuer->scheduled; + bool is_unbound = wq->flags & WQ_UNBOUND; unsigned int cpu; set_user_nice(current, RESCUER_NICE_LEVEL); @@ -1891,8 +1971,13 @@ repeat: if (kthread_should_stop()) return 0; + /* + * See whether any cpu is asking for help. Unbounded + * workqueues use cpu 0 in mayday_mask for CPU_UNBOUND. + */ for_each_cpu(cpu, wq->mayday_mask) { - struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); + unsigned int tcpu = is_unbound ? WORK_CPU_UNBOUND : cpu; + struct cpu_workqueue_struct *cwq = get_cwq(tcpu, wq); struct global_cwq *gcwq = cwq->gcwq; struct work_struct *work, *n; @@ -2034,7 +2119,7 @@ static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq, atomic_set(&wq->nr_cwqs_to_flush, 1); } - for_each_possible_cpu(cpu) { + for_each_cwq_cpu(cpu, wq) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); struct global_cwq *gcwq = cwq->gcwq; @@ -2344,7 +2429,7 @@ static void wait_on_work(struct work_struct *work) lock_map_acquire(&work->lockdep_map); lock_map_release(&work->lockdep_map); - for_each_possible_cpu(cpu) + for_each_gcwq_cpu(cpu) wait_on_cpu_work(get_gcwq(cpu), work); } @@ -2590,23 +2675,25 @@ static int alloc_cwqs(struct workqueue_struct *wq) const size_t size = sizeof(struct cpu_workqueue_struct); const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS, __alignof__(unsigned long long)); -#ifndef CONFIG_SMP - void *ptr; - /* - * Allocate enough room to align cwq and put an extra pointer - * at the end pointing back to the originally allocated - * pointer which will be used for free. - */ - ptr = kzalloc(size + align + sizeof(void *), GFP_KERNEL); - if (ptr) { - wq->cpu_wq.single = PTR_ALIGN(ptr, align); - *(void **)(wq->cpu_wq.single + 1) = ptr; + if (CONFIG_SMP && !(wq->flags & WQ_UNBOUND)) { + /* on SMP, percpu allocator can align itself */ + wq->cpu_wq.pcpu = __alloc_percpu(size, align); + } else { + void *ptr; + + /* + * Allocate enough room to align cwq and put an extra + * pointer at the end pointing back to the originally + * allocated pointer which will be used for free. + */ + ptr = kzalloc(size + align + sizeof(void *), GFP_KERNEL); + if (ptr) { + wq->cpu_wq.single = PTR_ALIGN(ptr, align); + *(void **)(wq->cpu_wq.single + 1) = ptr; + } } -#else - /* On SMP, percpu allocator can align itself */ - wq->cpu_wq.pcpu = __alloc_percpu(size, align); -#endif + /* just in case, make sure it's actually aligned */ BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align)); return wq->cpu_wq.v ? 0 : -ENOMEM; @@ -2614,23 +2701,25 @@ static int alloc_cwqs(struct workqueue_struct *wq) static void free_cwqs(struct workqueue_struct *wq) { -#ifndef CONFIG_SMP - /* on UP, the pointer to free is stored right after the cwq */ - if (wq->cpu_wq.single) + if (CONFIG_SMP && !(wq->flags & WQ_UNBOUND)) + free_percpu(wq->cpu_wq.pcpu); + else if (wq->cpu_wq.single) { + /* the pointer to free is stored right after the cwq */ kfree(*(void **)(wq->cpu_wq.single + 1)); -#else - free_percpu(wq->cpu_wq.pcpu); -#endif + } } -static int wq_clamp_max_active(int max_active, const char *name) +static int wq_clamp_max_active(int max_active, unsigned int flags, + const char *name) { - if (max_active < 1 || max_active > WQ_MAX_ACTIVE) + int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE; + + if (max_active < 1 || max_active > lim) printk(KERN_WARNING "workqueue: max_active %d requested for %s " "is out of range, clamping between %d and %d\n", - max_active, name, 1, WQ_MAX_ACTIVE); + max_active, name, 1, lim); - return clamp_val(max_active, 1, WQ_MAX_ACTIVE); + return clamp_val(max_active, 1, lim); } struct workqueue_struct *__alloc_workqueue_key(const char *name, @@ -2642,8 +2731,15 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name, struct workqueue_struct *wq; unsigned int cpu; + /* + * Unbound workqueues aren't concurrency managed and should be + * dispatched to workers immediately. + */ + if (flags & WQ_UNBOUND) + flags |= WQ_HIGHPRI; + max_active = max_active ?: WQ_DFL_ACTIVE; - max_active = wq_clamp_max_active(max_active, name); + max_active = wq_clamp_max_active(max_active, flags, name); wq = kzalloc(sizeof(*wq), GFP_KERNEL); if (!wq) @@ -2664,7 +2760,7 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name, if (alloc_cwqs(wq) < 0) goto err; - for_each_possible_cpu(cpu) { + for_each_cwq_cpu(cpu, wq) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); struct global_cwq *gcwq = get_gcwq(cpu); @@ -2703,7 +2799,7 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name, spin_lock(&workqueue_lock); if (workqueue_freezing && wq->flags & WQ_FREEZEABLE) - for_each_possible_cpu(cpu) + for_each_cwq_cpu(cpu, wq) get_cwq(cpu, wq)->max_active = 0; list_add(&wq->list, &workqueues); @@ -2743,7 +2839,7 @@ void destroy_workqueue(struct workqueue_struct *wq) spin_unlock(&workqueue_lock); /* sanity check */ - for_each_possible_cpu(cpu) { + for_each_cwq_cpu(cpu, wq) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); int i; @@ -2777,13 +2873,13 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active) { unsigned int cpu; - max_active = wq_clamp_max_active(max_active, wq->name); + max_active = wq_clamp_max_active(max_active, wq->flags, wq->name); spin_lock(&workqueue_lock); wq->saved_max_active = max_active; - for_each_possible_cpu(cpu) { + for_each_cwq_cpu(cpu, wq) { struct global_cwq *gcwq = get_gcwq(cpu); spin_lock_irq(&gcwq->lock); @@ -3310,7 +3406,7 @@ void freeze_workqueues_begin(void) BUG_ON(workqueue_freezing); workqueue_freezing = true; - for_each_possible_cpu(cpu) { + for_each_gcwq_cpu(cpu) { struct global_cwq *gcwq = get_gcwq(cpu); struct workqueue_struct *wq; @@ -3322,7 +3418,7 @@ void freeze_workqueues_begin(void) list_for_each_entry(wq, &workqueues, list) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); - if (wq->flags & WQ_FREEZEABLE) + if (cwq && wq->flags & WQ_FREEZEABLE) cwq->max_active = 0; } @@ -3354,7 +3450,7 @@ bool freeze_workqueues_busy(void) BUG_ON(!workqueue_freezing); - for_each_possible_cpu(cpu) { + for_each_gcwq_cpu(cpu) { struct workqueue_struct *wq; /* * nr_active is monotonically decreasing. It's safe @@ -3363,7 +3459,7 @@ bool freeze_workqueues_busy(void) list_for_each_entry(wq, &workqueues, list) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); - if (!(wq->flags & WQ_FREEZEABLE)) + if (!cwq || !(wq->flags & WQ_FREEZEABLE)) continue; BUG_ON(cwq->nr_active < 0); @@ -3396,7 +3492,7 @@ void thaw_workqueues(void) if (!workqueue_freezing) goto out_unlock; - for_each_possible_cpu(cpu) { + for_each_gcwq_cpu(cpu) { struct global_cwq *gcwq = get_gcwq(cpu); struct workqueue_struct *wq; @@ -3408,7 +3504,7 @@ void thaw_workqueues(void) list_for_each_entry(wq, &workqueues, list) { struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq); - if (!(wq->flags & WQ_FREEZEABLE)) + if (!cwq || !(wq->flags & WQ_FREEZEABLE)) continue; /* restore max_active and repopulate worklist */ @@ -3451,12 +3547,14 @@ void __init init_workqueues(void) hotcpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE); /* initialize gcwqs */ - for_each_possible_cpu(cpu) { + for_each_gcwq_cpu(cpu) { struct global_cwq *gcwq = get_gcwq(cpu); spin_lock_init(&gcwq->lock); INIT_LIST_HEAD(&gcwq->worklist); gcwq->cpu = cpu; + if (cpu == WORK_CPU_UNBOUND) + gcwq->flags |= GCWQ_DISASSOCIATED; INIT_LIST_HEAD(&gcwq->idle_list); for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++) @@ -3476,7 +3574,7 @@ void __init init_workqueues(void) } /* create the initial worker */ - for_each_online_cpu(cpu) { + for_each_online_gcwq_cpu(cpu) { struct global_cwq *gcwq = get_gcwq(cpu); struct worker *worker; @@ -3490,5 +3588,7 @@ void __init init_workqueues(void) system_wq = alloc_workqueue("events", 0, 0); system_long_wq = alloc_workqueue("events_long", 0, 0); system_nrt_wq = alloc_workqueue("events_nrt", WQ_NON_REENTRANT, 0); + system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND, + WQ_UNBOUND_MAX_ACTIVE); BUG_ON(!system_wq || !system_long_wq || !system_nrt_wq); } -- 2.41.0