workqueue: pick cwq instead of pool in __queue_work()

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.

tj: The original patch had two get_cwq() calls - the first to
    determine the pool by doing get_cwq(cpu, wq)->pool and the second
    to determine the matching cwq from get_cwq(pool->cpu, wq).
    Updated the function such that it chooses cwq instead of pool and
    removed the second call.  Rewrote the description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1801c37..d6fdce1 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1193,8 +1193,6 @@ static bool is_chained_work(struct workqueue_struct *wq)
 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 cpu, struct workqueue_struct *wq,
            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 cpu, struct workqueue_struct *wq,
                 * 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 cpu, struct workqueue_struct *wq,
 
        insert_work(cwq, work, worklist, work_flags);
 
-       spin_unlock(&pool->lock);
+       spin_unlock(&cwq->pool->lock);
 }
 
 /**