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workqueue: introduce worker
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Separate out worker thread related information to struct worker from
struct cpu_workqueue_struct and implement helper functions to deal
with the new struct worker.  The only change which is visible outside
is that now workqueue worker are all named "kworker/CPUID:WORKERID"
where WORKERID is allocated from per-cpu ida.

This is in preparation of concurrency managed workqueue where shared
multiple workers would be available per cpu.

Signed-off-by: Tejun Heo <tj@kernel.org>
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Tejun Heo committed Jun 29, 2010
1 parent 73f53c4 commit c34056a
Showing 1 changed file with 150 additions and 61 deletions.
211 changes: 150 additions & 61 deletions kernel/workqueue.c
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
#include <linux/kallsyms.h>
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>

/*
* Structure fields follow one of the following exclusion rules.
Expand All @@ -46,6 +47,15 @@
* W: workqueue_lock protected.
*/

struct cpu_workqueue_struct;

struct worker {
struct work_struct *current_work; /* L: work being processed */
struct task_struct *task; /* I: worker task */
struct cpu_workqueue_struct *cwq; /* I: the associated cwq */
int id; /* I: worker id */
};

/*
* The per-CPU workqueue (if single thread, we always use the first
* possible cpu). The lower WORK_STRUCT_FLAG_BITS of
Expand All @@ -58,15 +68,14 @@ struct cpu_workqueue_struct {

struct list_head worklist;
wait_queue_head_t more_work;
struct work_struct *current_work;
unsigned int cpu;
struct worker *worker;

struct workqueue_struct *wq; /* I: the owning workqueue */
int work_color; /* L: current color */
int flush_color; /* L: flushing color */
int nr_in_flight[WORK_NR_COLORS];
/* L: nr of in_flight works */
struct task_struct *thread;
};

/*
Expand Down Expand Up @@ -214,6 +223,9 @@ static inline void debug_work_deactivate(struct work_struct *work) { }
/* Serializes the accesses to the list of workqueues. */
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static DEFINE_PER_CPU(struct ida, worker_ida);

static int worker_thread(void *__worker);

static int singlethread_cpu __read_mostly;

Expand Down Expand Up @@ -428,6 +440,105 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
}
EXPORT_SYMBOL_GPL(queue_delayed_work_on);

static struct worker *alloc_worker(void)
{
struct worker *worker;

worker = kzalloc(sizeof(*worker), GFP_KERNEL);
return worker;
}

/**
* create_worker - create a new workqueue worker
* @cwq: cwq the new worker will belong to
* @bind: whether to set affinity to @cpu or not
*
* Create a new worker which is bound to @cwq. The returned worker
* can be started by calling start_worker() or destroyed using
* destroy_worker().
*
* CONTEXT:
* Might sleep. Does GFP_KERNEL allocations.
*
* RETURNS:
* Pointer to the newly created worker.
*/
static struct worker *create_worker(struct cpu_workqueue_struct *cwq, bool bind)
{
int id = -1;
struct worker *worker = NULL;

spin_lock(&workqueue_lock);
while (ida_get_new(&per_cpu(worker_ida, cwq->cpu), &id)) {
spin_unlock(&workqueue_lock);
if (!ida_pre_get(&per_cpu(worker_ida, cwq->cpu), GFP_KERNEL))
goto fail;
spin_lock(&workqueue_lock);
}
spin_unlock(&workqueue_lock);

worker = alloc_worker();
if (!worker)
goto fail;

worker->cwq = cwq;
worker->id = id;

worker->task = kthread_create(worker_thread, worker, "kworker/%u:%d",
cwq->cpu, id);
if (IS_ERR(worker->task))
goto fail;

if (bind)
kthread_bind(worker->task, cwq->cpu);

return worker;
fail:
if (id >= 0) {
spin_lock(&workqueue_lock);
ida_remove(&per_cpu(worker_ida, cwq->cpu), id);
spin_unlock(&workqueue_lock);
}
kfree(worker);
return NULL;
}

/**
* start_worker - start a newly created worker
* @worker: worker to start
*
* Start @worker.
*
* CONTEXT:
* spin_lock_irq(cwq->lock).
*/
static void start_worker(struct worker *worker)
{
wake_up_process(worker->task);
}

/**
* destroy_worker - destroy a workqueue worker
* @worker: worker to be destroyed
*
* Destroy @worker.
*/
static void destroy_worker(struct worker *worker)
{
int cpu = worker->cwq->cpu;
int id = worker->id;

/* sanity check frenzy */
BUG_ON(worker->current_work);

kthread_stop(worker->task);
kfree(worker);

spin_lock(&workqueue_lock);
ida_remove(&per_cpu(worker_ida, cpu), id);
spin_unlock(&workqueue_lock);
}

/**
* cwq_dec_nr_in_flight - decrement cwq's nr_in_flight
* @cwq: cwq of interest
Expand Down Expand Up @@ -468,7 +579,7 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color)

/**
* process_one_work - process single work
* @cwq: cwq to process work for
* @worker: self
* @work: work to process
*
* Process @work. This function contains all the logics necessary to
Expand All @@ -480,9 +591,9 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color)
* CONTEXT:
* spin_lock_irq(cwq->lock) which is released and regrabbed.
*/
static void process_one_work(struct cpu_workqueue_struct *cwq,
struct work_struct *work)
static void process_one_work(struct worker *worker, struct work_struct *work)
{
struct cpu_workqueue_struct *cwq = worker->cwq;
work_func_t f = work->func;
int work_color;
#ifdef CONFIG_LOCKDEP
Expand All @@ -497,7 +608,7 @@ static void process_one_work(struct cpu_workqueue_struct *cwq,
#endif
/* claim and process */
debug_work_deactivate(work);
cwq->current_work = work;
worker->current_work = work;
work_color = get_work_color(work);
list_del_init(&work->entry);

Expand All @@ -524,30 +635,33 @@ static void process_one_work(struct cpu_workqueue_struct *cwq,
spin_lock_irq(&cwq->lock);

/* we're done with it, release */
cwq->current_work = NULL;
worker->current_work = NULL;
cwq_dec_nr_in_flight(cwq, work_color);
}

static void run_workqueue(struct cpu_workqueue_struct *cwq)
static void run_workqueue(struct worker *worker)
{
struct cpu_workqueue_struct *cwq = worker->cwq;

spin_lock_irq(&cwq->lock);
while (!list_empty(&cwq->worklist)) {
struct work_struct *work = list_entry(cwq->worklist.next,
struct work_struct, entry);
process_one_work(cwq, work);
process_one_work(worker, work);
}
spin_unlock_irq(&cwq->lock);
}

/**
* worker_thread - the worker thread function
* @__cwq: cwq to serve
* @__worker: self
*
* The cwq worker thread function.
*/
static int worker_thread(void *__cwq)
static int worker_thread(void *__worker)
{
struct cpu_workqueue_struct *cwq = __cwq;
struct worker *worker = __worker;
struct cpu_workqueue_struct *cwq = worker->cwq;
DEFINE_WAIT(wait);

if (cwq->wq->flags & WQ_FREEZEABLE)
Expand All @@ -566,11 +680,11 @@ static int worker_thread(void *__cwq)
if (kthread_should_stop())
break;

if (unlikely(!cpumask_equal(&cwq->thread->cpus_allowed,
if (unlikely(!cpumask_equal(&worker->task->cpus_allowed,
get_cpu_mask(cwq->cpu))))
set_cpus_allowed_ptr(cwq->thread,
set_cpus_allowed_ptr(worker->task,
get_cpu_mask(cwq->cpu));
run_workqueue(cwq);
run_workqueue(worker);
}

return 0;
Expand Down Expand Up @@ -873,7 +987,7 @@ int flush_work(struct work_struct *work)
goto already_gone;
prev = &work->entry;
} else {
if (cwq->current_work != work)
if (!cwq->worker || cwq->worker->current_work != work)
goto already_gone;
prev = &cwq->worklist;
}
Expand Down Expand Up @@ -937,7 +1051,7 @@ static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
int running = 0;

spin_lock_irq(&cwq->lock);
if (unlikely(cwq->current_work == work)) {
if (unlikely(cwq->worker && cwq->worker->current_work == work)) {
insert_wq_barrier(cwq, &barr, cwq->worklist.next);
running = 1;
}
Expand Down Expand Up @@ -1225,7 +1339,7 @@ int current_is_keventd(void)
BUG_ON(!keventd_wq);

cwq = get_cwq(cpu, keventd_wq);
if (current == cwq->thread)
if (current == cwq->worker->task)
ret = 1;

return ret;
Expand Down Expand Up @@ -1279,46 +1393,15 @@ static void free_cwqs(struct cpu_workqueue_struct *cwqs)
#endif
}

static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
{
struct workqueue_struct *wq = cwq->wq;
struct task_struct *p;

p = kthread_create(worker_thread, cwq, "%s/%d", 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);
cwq->thread = p;

return 0;
}

static void start_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
{
struct task_struct *p = cwq->thread;

if (p != NULL) {
if (cpu >= 0)
kthread_bind(p, cpu);
wake_up_process(p);
}
}

struct workqueue_struct *__create_workqueue_key(const char *name,
unsigned int flags,
struct lock_class_key *key,
const char *lock_name)
{
bool singlethread = flags & WQ_SINGLE_THREAD;
struct workqueue_struct *wq;
int err = 0, cpu;
bool failed = false;
unsigned int cpu;

wq = kzalloc(sizeof(*wq), GFP_KERNEL);
if (!wq)
Expand Down Expand Up @@ -1348,20 +1431,21 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);

BUG_ON((unsigned long)cwq & WORK_STRUCT_FLAG_MASK);
cwq->wq = wq;
cwq->cpu = cpu;
cwq->wq = wq;
cwq->flush_color = -1;
spin_lock_init(&cwq->lock);
INIT_LIST_HEAD(&cwq->worklist);
init_waitqueue_head(&cwq->more_work);

if (err)
if (failed)
continue;
err = create_workqueue_thread(cwq, cpu);
if (cpu_online(cpu) && !singlethread)
start_workqueue_thread(cwq, cpu);
cwq->worker = create_worker(cwq,
cpu_online(cpu) && !singlethread);
if (cwq->worker)
start_worker(cwq->worker);
else
start_workqueue_thread(cwq, -1);
failed = true;
}

spin_lock(&workqueue_lock);
Expand All @@ -1370,7 +1454,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,

cpu_maps_update_done();

if (err) {
if (failed) {
destroy_workqueue(wq);
wq = NULL;
}
Expand Down Expand Up @@ -1406,9 +1490,9 @@ void destroy_workqueue(struct workqueue_struct *wq)
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
int i;

if (cwq->thread) {
kthread_stop(cwq->thread);
cwq->thread = NULL;
if (cwq->worker) {
destroy_worker(cwq->worker);
cwq->worker = NULL;
}

for (i = 0; i < WORK_NR_COLORS; i++)
Expand Down Expand Up @@ -1495,6 +1579,11 @@ EXPORT_SYMBOL_GPL(work_on_cpu);

void __init init_workqueues(void)
{
unsigned int cpu;

for_each_possible_cpu(cpu)
ida_init(&per_cpu(worker_ida, cpu));

singlethread_cpu = cpumask_first(cpu_possible_mask);
hotcpu_notifier(workqueue_cpu_callback, 0);
keventd_wq = create_workqueue("events");
Expand Down

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