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Subject[PATCH 3/3] workqueue: unfold start_worker() into create_worker()
Date
Simply unfold the code of start_worker() into create_worker() and
remove the original start_worker() and create_and_start_worker().

maybe_create_worker() also becomes decently shorter.

The only trade-off is the introduced overhead that the pool->lock
is released and regrabbed after the newly worker is started.
The overhead is acceptible since the manager is slow path.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
kernel/workqueue.c | 68 ++++++++++------------------------------------------
1 files changed, 13 insertions(+), 55 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4fdd6d0..c820057 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1553,7 +1553,7 @@ static void worker_enter_idle(struct worker *worker)
(worker->hentry.next || worker->hentry.pprev)))
return;

- /* can't use worker_set_flags(), also called from start_worker() */
+ /* can't use worker_set_flags(), also called from create_worker() */
worker->flags |= WORKER_IDLE;
pool->nr_idle++;
worker->last_active = jiffies;
@@ -1674,8 +1674,7 @@ static void worker_detach_from_pool(struct worker *worker,
* create_worker - create a new workqueue worker
* @pool: pool the new worker will belong to
*
- * Create a new worker which is attached to @pool. The new worker must be
- * started by start_worker().
+ * Create and start a new worker which is attached to @pool.
*
* CONTEXT:
* Might sleep. Does GFP_KERNEL allocations.
@@ -1720,6 +1719,13 @@ static struct worker *create_worker(struct worker_pool *pool)
/* successful, attach the worker to the pool */
worker_attach_to_pool(worker, pool);

+ /* start the newly created worker */
+ spin_lock_irq(&pool->lock);
+ worker->pool->nr_workers++;
+ worker_enter_idle(worker);
+ wake_up_process(worker->task);
+ spin_unlock_irq(&pool->lock);
+
return worker;

fail:
@@ -1730,44 +1736,6 @@ fail:
}

/**
- * start_worker - start a newly created worker
- * @worker: worker to start
- *
- * Make the pool aware of @worker and start it.
- *
- * CONTEXT:
- * spin_lock_irq(pool->lock).
- */
-static void start_worker(struct worker *worker)
-{
- worker->pool->nr_workers++;
- worker_enter_idle(worker);
- wake_up_process(worker->task);
-}
-
-/**
- * create_and_start_worker - create and start a worker for a pool
- * @pool: the target pool
- *
- * Grab the managership of @pool and create and start a new worker for it.
- *
- * Return: 0 on success. A negative error code otherwise.
- */
-static int create_and_start_worker(struct worker_pool *pool)
-{
- struct worker *worker;
-
- worker = create_worker(pool);
- if (worker) {
- spin_lock_irq(&pool->lock);
- start_worker(worker);
- spin_unlock_irq(&pool->lock);
- }
-
- return worker ? 0 : -ENOMEM;
-}
-
-/**
* destroy_worker - destroy a workqueue worker
* @worker: worker to be destroyed
*
@@ -1895,22 +1863,12 @@ static void maybe_create_worker(struct worker_pool *pool)
__releases(&pool->lock)
__acquires(&pool->lock)
{
- struct worker *worker;
-
spin_unlock_irq(&pool->lock);

/* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);

- worker = create_worker(pool);
- if (worker) {
- del_timer_sync(&pool->mayday_timer);
- spin_lock_irq(&pool->lock);
- start_worker(worker);
- return;
- }
-
- if (need_to_create_worker(pool))
+ if (!create_worker(pool) && need_to_create_worker(pool))
schedule_timeout_interruptible(CREATE_COOLDOWN);

del_timer_sync(&pool->mayday_timer);
@@ -3524,7 +3482,7 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
goto fail;

/* create and start the initial worker */
- if (create_and_start_worker(pool) < 0)
+ if (!create_worker(pool))
goto fail;

/* install */
@@ -4598,7 +4556,7 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
for_each_cpu_worker_pool(pool, cpu) {
if (pool->nr_workers)
continue;
- if (create_and_start_worker(pool) < 0)
+ if (!create_worker(pool))
return NOTIFY_BAD;
}
break;
@@ -4898,7 +4856,7 @@ static int __init init_workqueues(void)

for_each_cpu_worker_pool(pool, cpu) {
pool->flags &= ~POOL_DISASSOCIATED;
- BUG_ON(create_and_start_worker(pool) < 0);
+ BUG_ON(!create_worker(pool));
}
}

--
1.7.4.4


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