[PATCH 19/21] workqueue: introduce worker

Tejun Heo
2009-11-16T17:18:42Z

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 | 219 +++++++++++++++++++++++++++++++++++++---------------
1 files changed, 157 insertions(+), 62 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index dce5ad5..6694b3e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -34,6 +34,7 @@
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/mutex.h>
+#include <linux/idr.h>

/*
* Structure fields follow one of the following exclusion rules.
@@ -47,6 +48,15 @@
* 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
@@ -59,14 +69,14 @@ 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_COLORS];
/* L: nr of in_flight works */
- struct task_struct *thread;
} __attribute__((aligned(1 << WORK_STRUCT_FLAG_BITS)));

/*
@@ -215,6 +225,9 @@ 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 struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
struct workqueue_struct *wq)
@@ -413,6 +426,105 @@ 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_irq(&workqueue_lock);
+ if (!ida_pre_get(&per_cpu(worker_ida, cwq->cpu), GFP_KERNEL))
+ goto fail;
+ spin_lock(&workqueue_lock);
+ }
+ spin_unlock_irq(&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_irq(&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_irq(&workqueue_lock);
+ ida_remove(&per_cpu(worker_ida, cpu), id);
+ spin_unlock_irq(&workqueue_lock);
+}
+
/**
* cwq_dec_nr_in_flight - decrement cwq's nr_in_flight
* @cwq: cwq of interest
@@ -450,7 +562,7 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq,

/**
* 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
@@ -462,9 +574,9 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq,
* 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;
struct workqueue_struct *wq = cwq->wq;
bool single_thread = wq->flags & WQ_SINGLE_THREAD;
work_func_t f = work->func;
@@ -481,7 +593,7 @@ 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);

@@ -515,30 +627,33 @@ 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)
@@ -557,7 +672,7 @@ static int worker_thread(void *__cwq)
if (kthread_should_stop())
break;

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

return 0;
@@ -855,7 +970,7 @@ 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;
}
@@ -920,7 +1035,7 @@ 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;
}
@@ -1183,52 +1298,21 @@ 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;

}

-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)
{
struct workqueue_struct *wq;
- int err = 0, cpu;
+ bool failed = false;
+ unsigned int cpu;

wq = kzalloc(sizeof(*wq), GFP_KERNEL);
if (!wq)
@@ -1267,20 +1351,24 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
for_each_possible_cpu(cpu) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, 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 || !cpu_online(cpu))
+ if (failed || !cpu_online(cpu))
continue;
- err = create_workqueue_thread(cwq, cpu);
- start_workqueue_thread(cwq, cpu);
+ cwq->worker = create_worker(cwq, true);
+ if (cwq->worker)
+ start_worker(cwq->worker);
+ else
+ failed = true;
}
cpu_maps_update_done();

- if (err) {
+ if (failed) {
destroy_workqueue(wq);
wq = NULL;
}
@@ -1316,9 +1404,9 @@ void destroy_workqueue(struct workqueue_struct *wq)
int i;

/* cpu_add_remove_lock protects cwq->thread */
- 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_COLORS; i++)
@@ -1349,7 +1437,8 @@ undo:

switch (action) {
case CPU_UP_PREPARE:
- if (!create_workqueue_thread(cwq, cpu))
+ cwq->worker = create_worker(cwq, false);
+ if (cwq->worker)
break;
printk(KERN_ERR "workqueue [%s] for %i failed\n",
wq->name, cpu);
@@ -1358,17 +1447,18 @@ undo:
goto undo;

case CPU_ONLINE:
- start_workqueue_thread(cwq, cpu);
+ kthread_bind(cwq->worker->task, cpu);
+ start_worker(cwq->worker);
break;

case CPU_UP_CANCELED:
- start_workqueue_thread(cwq, -1);
+ start_worker(cwq->worker);
case CPU_POST_DEAD:
flush_workqueue(wq);
/* cpu_add_remove_lock protects cwq->thread */
- if (cwq->thread) {
- kthread_stop(cwq->thread);
- cwq->thread = NULL;
+ if (cwq->worker) {
+ destroy_worker(cwq->worker);
+ cwq->worker = NULL;
}
break;
}
@@ -1426,6 +1516,8 @@ 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
@@ -1435,6 +1527,9 @@ 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));
+
hotcpu_notifier(workqueue_cpu_callback, 0);
keventd_wq = create_workqueue("events");
BUG_ON(!keventd_wq);
--
1.6.4.2