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[PATCH 1/6] workqueue: don't use WQ_HIGHPRI for unbound workqueues

To: linux-kernel@xxxxxxxxxxxxxxx
Subject: [PATCH 1/6] workqueue: don't use WQ_HIGHPRI for unbound workqueues
From: Tejun Heo <tj@xxxxxxxxxx>
Date: Mon, 9 Jul 2012 11:41:50 -0700
Cc: torvalds@xxxxxxxxxxxxxxxxxxxx, joshhunt00@xxxxxxxxx, axboe@xxxxxxxxx, rni@xxxxxxxxxx, vgoyal@xxxxxxxxxx, vwadekar@xxxxxxxxxx, herbert@xxxxxxxxxxxxxxxxxxxx, davem@xxxxxxxxxxxxx, linux-crypto@xxxxxxxxxxxxxxx, swhiteho@xxxxxxxxxx, bpm@xxxxxxx, elder@xxxxxxxxxx, xfs@xxxxxxxxxxx, marcel@xxxxxxxxxxxx, gustavo@xxxxxxxxxxx, johan.hedberg@xxxxxxxxx, linux-bluetooth@xxxxxxxxxxxxxxx, martin.petersen@xxxxxxxxxx, Tejun Heo <tj@xxxxxxxxxx>
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Sender: Tejun Heo <htejun@xxxxxxxxx>
Unbound wqs aren't concurrency-managed and try to execute work items
as soon as possible.  This is currently achieved by implicitly setting
%WQ_HIGHPRI on all unbound workqueues; however, WQ_HIGHPRI
implementation is about to be restructured and this usage won't be
valid anymore.

Add an explicit chain-wakeup path for unbound workqueues in
process_one_work() instead of piggy backing on %WQ_HIGHPRI.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 kernel/workqueue.c |   18 +++++++++++-------
 1 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9a3128d..27637c2 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -580,6 +580,10 @@ static bool __need_more_worker(struct global_cwq *gcwq)
 /*
  * Need to wake up a worker?  Called from anything but currently
  * running workers.
+ *
+ * Note that, because unbound workers never contribute to nr_running, this
+ * function will always return %true for unbound gcwq as long as the
+ * worklist isn't empty.
  */
 static bool need_more_worker(struct global_cwq *gcwq)
 {
@@ -1867,6 +1871,13 @@ __acquires(&gcwq->lock)
        if (unlikely(cpu_intensive))
                worker_set_flags(worker, WORKER_CPU_INTENSIVE, true);
 
+       /*
+        * Unbound gcwq isn't concurrency managed and work items should be
+        * executed ASAP.  Wake up another worker if necessary.
+        */
+       if ((worker->flags & WORKER_UNBOUND) && need_more_worker(gcwq))
+               wake_up_worker(gcwq);
+
        spin_unlock_irq(&gcwq->lock);
 
        work_clear_pending(work);
@@ -2984,13 +2995,6 @@ struct workqueue_struct *__alloc_workqueue_key(const 
char *fmt,
        if (flags & WQ_MEM_RECLAIM)
                flags |= WQ_RESCUER;
 
-       /*
-        * Unbound workqueues aren't concurrency managed and should be
-        * dispatched to workers immediately.
-        */
-       if (flags & WQ_UNBOUND)
-               flags |= WQ_HIGHPRI;
-
        max_active = max_active ?: WQ_DFL_ACTIVE;
        max_active = wq_clamp_max_active(max_active, flags, wq->name);
 
-- 
1.7.7.3

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