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Subject[PATCH wq/for-3.9] workqueue: pick cwq instead of pool in __queue_work()
From: Lai Jiangshan <laijs@cn.fujitsu.com>

Currently, __queue_work() chooses the pool to queue a work item to and
then determines cwq from the target wq and the chosen pool. This is a
bit backwards in that we can determine cwq first and simply use
cwq->pool. This way, we can skip get_std_worker_pool() in queueing
path which will be a hurdle when implementing custom worker pools.

Update __queue_work() such that it chooses the target cwq and then use
cwq->pool instead of the other way around. While at it, add missing
{} in an if statement.

This patch doesn't introduce any functional changes.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1193,8 +1193,6 @@ static bool is_chained_work(struct workq
static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
- bool highpri = wq->flags & WQ_HIGHPRI;
- struct worker_pool *pool;
struct cpu_workqueue_struct *cwq;
struct list_head *worklist;
unsigned int work_flags;
@@ -1215,7 +1213,7 @@ static void __queue_work(unsigned int cp
WARN_ON_ONCE(!is_chained_work(wq)))
return;

- /* determine pool to use */
+ /* determine the cwq to use */
if (!(wq->flags & WQ_UNBOUND)) {
struct worker_pool *last_pool;

@@ -1228,37 +1226,36 @@ static void __queue_work(unsigned int cp
* work needs to be queued on that cpu to guarantee
* non-reentrancy.
*/
- pool = get_std_worker_pool(cpu, highpri);
+ cwq = get_cwq(cpu, wq);
last_pool = get_work_pool(work);

- if (last_pool && last_pool != pool) {
+ if (last_pool && last_pool != cwq->pool) {
struct worker *worker;

spin_lock(&last_pool->lock);

worker = find_worker_executing_work(last_pool, work);

- if (worker && worker->current_cwq->wq == wq)
- pool = last_pool;
- else {
+ if (worker && worker->current_cwq->wq == wq) {
+ cwq = get_cwq(last_pool->cpu, wq);
+ } else {
/* meh... not running there, queue here */
spin_unlock(&last_pool->lock);
- spin_lock(&pool->lock);
+ spin_lock(&cwq->pool->lock);
}
} else {
- spin_lock(&pool->lock);
+ spin_lock(&cwq->pool->lock);
}
} else {
- pool = get_std_worker_pool(WORK_CPU_UNBOUND, highpri);
- spin_lock(&pool->lock);
+ cwq = get_cwq(WORK_CPU_UNBOUND, wq);
+ spin_lock(&cwq->pool->lock);
}

- /* pool determined, get cwq and queue */
- cwq = get_cwq(pool->cpu, wq);
+ /* cwq determined, queue */
trace_workqueue_queue_work(req_cpu, cwq, work);

if (WARN_ON(!list_empty(&work->entry))) {
- spin_unlock(&pool->lock);
+ spin_unlock(&cwq->pool->lock);
return;
}

@@ -1276,7 +1273,7 @@ static void __queue_work(unsigned int cp

insert_work(cwq, work, worklist, work_flags);

- spin_unlock(&pool->lock);
+ spin_unlock(&cwq->pool->lock);
}

/**

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