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workqueue: implement unbound workqueue

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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 <tj@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: David Howells <dhowells@redhat.com>
This commit is contained in:
Tejun Heo 2010-07-02 10:03:51 +02:00
parent bdbc5dd7de
commit f34217977d
2 changed files with 173 additions and 60 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

15
include/linux/workqueue.h
View file

@ -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,

198
kernel/workqueue.c
View file

@ -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)
{
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)
{
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;
#else
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 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 */
@ -1166,6 +1231,7 @@ static bool worker_maybe_bind_and_lock(struct worker *worker)
* it races with cpu hotunplug operation. Verify
* against GCWQ_DISASSOCIATED.
*/
if (!(gcwq->flags & GCWQ_DISASSOCIATED))
set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));
spin_lock_irq(&gcwq->lock);
@ -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 @@ static int rescuer_thread(void *__wq)
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
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.
* 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)
kfree(*(void **)(wq->cpu_wq.single + 1));
#else
if (CONFIG_SMP && !(wq->flags & WQ_UNBOUND))
free_percpu(wq->cpu_wq.pcpu);
#endif
else if (wq->cpu_wq.single) {
/* the pointer to free is stored right after the cwq */
kfree(*(void **)(wq->cpu_wq.single + 1));
}
}
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);
}