[PATCH 17/27] workqueue: introduce worker

Tejun Heo
2009-12-18T13:03:50Z

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>
---
kernel/workqueue.c | 211 +++++++++++++++++++++++++++++++++++++---------------
1 files changed, 151 insertions(+), 60 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9e55c80..17d270b 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -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.
@@ -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
@@ -58,14 +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;
};

/*
@@ -213,6 +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;

@@ -420,6 +433,105 @@ 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
@@ -460,7 +572,7 @@ 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
@@ -472,9 +584,9 @@ 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
@@ -489,7 +601,7 @@ 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 = work_flags_to_color(*work_data_bits(work));
list_del_init(&work->entry);

@@ -516,30 +628,33 @@ 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)
@@ -558,7 +673,7 @@ static int worker_thread(void *__cwq)
if (kthread_should_stop())
break;

- run_workqueue(cwq);
+ run_workqueue(worker);
}

return 0;
@@ -856,7 +971,7 @@ 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;
}
@@ -921,7 +1036,7 @@ 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;
}
@@ -1184,7 +1299,7 @@ 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;
@@ -1229,38 +1344,6 @@ 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,
@@ -1268,7 +1351,8 @@ struct workqueue_struct *__create_workqueue_key(const char *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)
@@ -1298,23 +1382,25 @@ 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->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;
}
cpu_maps_update_done();

- if (err) {
+ if (failed) {
destroy_workqueue(wq);
wq = NULL;
}
@@ -1353,9 +1439,9 @@ 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++)
@@ -1385,8 +1471,8 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,

switch (action) {
case CPU_ONLINE:
- __set_cpus_allowed(cwq->thread, get_cpu_mask(cpu),
- true);
+ __set_cpus_allowed(cwq->worker->task,
+ get_cpu_mask(cpu), true);
break;

case CPU_POST_DEAD:
@@ -1447,6 +1533,8 @@ EXPORT_SYMBOL_GPL(work_on_cpu);

void __init init_workqueues(void)
{
+ unsigned int cpu;
+
/*
* cwqs are forced aligned according to WORK_STRUCT_FLAG_BITS.
* Make sure that the alignment isn't lower than that of
@@ -1455,6 +1543,9 @@ void __init init_workqueues(void)
BUILD_BUG_ON(__alignof__(struct cpu_workqueue_struct) <
__alignof__(unsigned long long));

+ 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");
--
1.6.4.2