From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH wq/for-3.9 workqueue]: add delayed_work->wq to simplify reentrancy handling
Date: Wed, 6 Feb 2013 16:28:06 -0800 [thread overview]
Message-ID: <20130207002806.GG2875@htj.dyndns.org> (raw)
In-Reply-To: <1359657696-2767-4-git-send-email-laijs@cn.fujitsu.com>
From: Lai Jiangshan <laijs@cn.fujitsu.com>
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>
---
include/linux/workqueue.h | 3 +++
kernel/workqueue.c | 32 +++-----------------------------
2 files changed, 6 insertions(+), 29 deletions(-)
--- 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;
};
--- 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 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
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_w
{
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);
}
next prev parent reply other threads:[~2013-02-07 0:28 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-31 18:41 [PATCH 00/13] workqueue: enhance locking and record global worker id for work data Lai Jiangshan
2013-01-31 18:41 ` [PATCH 01/13] workqueue: remove WORK_CPU_NONE Lai Jiangshan
2013-02-04 19:49 ` Tejun Heo
2013-02-05 12:03 ` Lai Jiangshan
2013-02-06 22:34 ` [PATCH wq/for-3.9] workqueue: replace WORK_CPU_NONE/LAST with WORK_CPU_END Tejun Heo
2013-01-31 18:41 ` [PATCH 02/13] workqueue: fix work_busy() Lai Jiangshan
2013-02-04 19:54 ` Tejun Heo
2013-02-05 12:06 ` Lai Jiangshan
2013-02-05 18:53 ` Tejun Heo
2013-02-06 11:42 ` Lai Jiangshan
2013-02-06 14:05 ` Tejun Heo
2013-02-06 23:02 ` [PATCH wq/for-3.9] workqueue: make work_busy() test WORK_STRUCT_PENDING first Tejun Heo
2013-01-31 18:41 ` [PATCH 03/13] workqueue: don't set work cwq until we queued it on pool Lai Jiangshan
2013-02-04 21:28 ` Tejun Heo
2013-02-05 15:00 ` Lai Jiangshan
2013-02-05 16:45 ` Tejun Heo
2013-02-06 11:35 ` Lai Jiangshan
2013-02-06 14:18 ` Tejun Heo
2013-02-05 15:06 ` Lai Jiangshan
2013-02-07 0:28 ` Tejun Heo [this message]
2013-01-31 18:41 ` [PATCH 04/13] workqueue: clear cwq when cancel the work Lai Jiangshan
2013-02-07 0:53 ` [PATCH wq/for-3.9] workqueue: make work->data point to pool after try_to_grab_pending() Tejun Heo
2013-01-31 18:41 ` [PATCH 05/13] workqueue: change queued detection and remove *mb()s Lai Jiangshan
2013-02-07 1:52 ` [PATCH wq/for-3.9] workqueue: simplify is-work-item-queued-here test Tejun Heo
2013-02-07 2:03 ` [PATCH wq/for-3.9] workqueue: cosmetic update in try_to_grab_pending() Tejun Heo
2013-01-31 18:41 ` [PATCH 06/13] workqueue: get pool id from work->data directly if it is offq Lai Jiangshan
2013-02-07 20:16 ` [PATCH wq/for-3.9] workqueue: make get_work_pool_id() cheaper Tejun Heo
2013-01-31 18:41 ` [PATCH 07/13] workqueue: get pool from wq/cwq Lai Jiangshan
2013-02-07 21:13 ` [PATCH wq/for-3.9] workqueue: pick cwq instead of pool in __queue_work() Tejun Heo
2013-01-31 18:41 ` [PATCH 08/13] workqueue: add lock_pool_executing_work() Lai Jiangshan
2013-02-04 21:34 ` Tejun Heo
2013-02-05 12:15 ` Lai Jiangshan
2013-02-05 19:09 ` Tejun Heo
2013-01-31 18:41 ` [PATCH 09/13] workqueue: add lock_pool_queued_work() Lai Jiangshan
2013-01-31 18:41 ` [PATCH 10/13] workqueue: add lock_pool_own_work() and remove get_work_pool() Lai Jiangshan
2013-02-04 21:38 ` Tejun Heo
2013-01-31 18:41 ` [PATCH 11/13] workqueue: allow more work_pool id space Lai Jiangshan
2013-01-31 18:41 ` [PATCH 12/13] workqueue: add worker's global worker ID Lai Jiangshan
2013-02-04 21:39 ` Tejun Heo
2013-01-31 18:41 ` [PATCH 13/13] workqueue: record global worker ID instead of pool ID in work->data when off-queue Lai Jiangshan
2013-02-04 21:40 ` Tejun Heo
2013-02-04 22:12 ` Tejun Heo
2013-02-05 15:18 ` Lai Jiangshan
2013-02-07 22:02 ` Tejun Heo
2013-02-13 22:23 ` Tejun Heo
2013-02-04 21:04 ` [PATCH 00/13] workqueue: enhance locking and record global worker id for work data Tejun Heo
2013-02-05 16:19 ` Lai Jiangshan
2013-02-05 16:50 ` Tejun Heo
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