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author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2013-02-07 02:04:53 (GMT) |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2013-02-07 02:04:53 (GMT) |
commit | 60c057bca22285efefbba033624763a778f243bf (patch) | |
tree | 8e469c390b5b60ad6b4d7c94bc07522f857032bc | |
parent | 038366c5cf23ae737b9f72169dd8ade2d105755b (diff) | |
download | linux-fsl-qoriq-60c057bca22285efefbba033624763a778f243bf.tar.xz |
workqueue: add delayed_work->wq to simplify reentrancy handling
To avoid executing the same work item from multiple CPUs concurrently,
a work_struct records the last pool it was on in its ->data so that,
on the next queueing, the pool can be queried to determine whether the
work item is still executing or not.
A delayed_work goes through timer before actually being queued on the
target workqueue and the timer needs to know the target workqueue and
CPU. This is currently achieved by modifying delayed_work->work.data
such that it points to the cwq which points to the target workqueue
and the last CPU the work item was on. __queue_delayed_work()
extracts the last CPU from delayed_work->work.data and then combines
it with the target workqueue to create new work.data.
The only thing this rather ugly hack achieves is encoding the target
workqueue into delayed_work->work.data without using a separate field,
which could be a trade off one can make; unfortunately, this entangles
work->data management between regular workqueue and delayed_work code
by setting cwq pointer before the work item is actually queued and
becomes a hindrance for further improvements of work->data handling.
This can be easily made sane by adding a target workqueue field to
delayed_work. While delayed_work is used widely in the kernel and
this does make it a bit larger (<5%), I think this is the right
trade-off especially given the prospect of much saner handling of
work->data which currently involves quite tricky memory barrier
dancing, and don't expect to see any measureable effect.
Add delayed_work->wq and drop the delayed_work->work.data overloading.
tj: Rewrote the description.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
-rw-r--r-- | include/linux/workqueue.h | 3 | ||||
-rw-r--r-- | kernel/workqueue.c | 32 |
2 files changed, 6 insertions, 29 deletions
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index 426c39c..a3d7556 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -109,6 +109,9 @@ struct work_struct { struct delayed_work { struct work_struct work; struct timer_list timer; + + /* target workqueue and CPU ->timer uses to queue ->work */ + struct workqueue_struct *wq; int cpu; }; diff --git a/kernel/workqueue.c b/kernel/workqueue.c index a229a56..41a502c 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1339,10 +1339,9 @@ EXPORT_SYMBOL_GPL(queue_work); void delayed_work_timer_fn(unsigned long __data) { struct delayed_work *dwork = (struct delayed_work *)__data; - struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work); /* should have been called from irqsafe timer with irq already off */ - __queue_work(dwork->cpu, cwq->wq, &dwork->work); + __queue_work(dwork->cpu, dwork->wq, &dwork->work); } EXPORT_SYMBOL_GPL(delayed_work_timer_fn); @@ -1351,7 +1350,6 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq, { struct timer_list *timer = &dwork->timer; struct work_struct *work = &dwork->work; - unsigned int lcpu; WARN_ON_ONCE(timer->function != delayed_work_timer_fn || timer->data != (unsigned long)dwork); @@ -1371,30 +1369,7 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq, timer_stats_timer_set_start_info(&dwork->timer); - /* - * This stores cwq for the moment, for the timer_fn. Note that the - * work's pool is preserved to allow reentrance detection for - * delayed works. - */ - if (!(wq->flags & WQ_UNBOUND)) { - struct worker_pool *pool = get_work_pool(work); - - /* - * If we cannot get the last pool from @work directly, - * select the last CPU such that it avoids unnecessarily - * triggering non-reentrancy check in __queue_work(). - */ - lcpu = cpu; - if (pool) - lcpu = pool->cpu; - if (lcpu == WORK_CPU_UNBOUND) - lcpu = raw_smp_processor_id(); - } else { - lcpu = WORK_CPU_UNBOUND; - } - - set_work_cwq(work, get_cwq(lcpu, wq), 0); - + dwork->wq = wq; dwork->cpu = cpu; timer->expires = jiffies + delay; @@ -2944,8 +2919,7 @@ bool flush_delayed_work(struct delayed_work *dwork) { local_irq_disable(); if (del_timer_sync(&dwork->timer)) - __queue_work(dwork->cpu, - get_work_cwq(&dwork->work)->wq, &dwork->work); + __queue_work(dwork->cpu, dwork->wq, &dwork->work); local_irq_enable(); return flush_work(&dwork->work); } |