From 0e0cafcda83951bb0b438d78a4216ae94483cba6 Mon Sep 17 00:00:00 2001
From: Alexei Potashnik <alexei@purestorage.com>
Date: Tue, 18 Jul 2017 11:12:53 -0700
Subject: [PATCH 1/4] workqueue: doc change for ST behavior on NUMA systems
NUMA rework of workqueue made the combination of max_active of 1 and
WQ_UNBOUND insufficient to guarantee ST behavior system wide.
alloc_ordered_queue should now be used instead.
Signed-off-by: Alexei Potashnik <alexei@purestorage.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
Documentation/core-api/workqueue.rst | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index ffdec94fbca1..3943b5bfa8cf 100644
--- a/Documentation/core-api/workqueue.rst
+++ b/Documentation/core-api/workqueue.rst
@@ -243,11 +243,15 @@ throttling the number of active work items, specifying '0' is
recommended.
Some users depend on the strict execution ordering of ST wq. The
-combination of ``@max_active`` of 1 and ``WQ_UNBOUND`` is used to
-achieve this behavior. Work items on such wq are always queued to the
-unbound worker-pools and only one work item can be active at any given
+combination of ``@max_active`` of 1 and ``WQ_UNBOUND`` used to
+achieve this behavior. Work items on such wq were always queued to the
+unbound worker-pools and only one work item could be active at any given
time thus achieving the same ordering property as ST wq.
+In the current implementation the above configuration only guarantees
+ST behavior within a given NUMA node. Instead alloc_ordered_queue should
+be used to achieve system wide ST behavior.
+
Example Execution Scenarios
===========================
From 9a2614916ac564d6ea1d0a5cb986298bc508c3bf Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <bp@benjamin.pe>
Date: Sun, 6 Aug 2017 19:33:22 -0700
Subject: [PATCH 2/4] workqueue: fix path to documentation
Signed-off-by: Benjamin Peterson <bp@benjamin.pe>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a86688fabc55..4fa6c7650f09 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -21,7 +21,7 @@
* pools for workqueues which are not bound to any specific CPU - the
* number of these backing pools is dynamic.
*
- * Please read Documentation/workqueue.txt for details.
+ * Please read Documentation/core-api/workqueue.rst for details.
*/
#include <linux/export.h>
From c5a94a618e7ac86b20f53d947f68d7cee6a4c6bc Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 23 Aug 2017 13:58:44 +0200
Subject: [PATCH 3/4] workqueue: Use TASK_IDLE
Workqueues don't use signals, it (ab)uses TASK_INTERRUPTIBLE to avoid
increasing the loadavg numbers. We've 'recently' introduced TASK_IDLE
for this case:
80ed87c8a9ca ("sched/wait: Introduce TASK_NOLOAD and TASK_IDLE")
use it.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4fa6c7650f09..2d278b9a5469 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2247,7 +2247,7 @@ sleep:
* event.
*/
worker_enter_idle(worker);
- __set_current_state(TASK_INTERRUPTIBLE);
+ __set_current_state(TASK_IDLE);
spin_unlock_irq(&pool->lock);
schedule();
goto woke_up;
@@ -2289,7 +2289,7 @@ static int rescuer_thread(void *__rescuer)
*/
rescuer->task->flags |= PF_WQ_WORKER;
repeat:
- set_current_state(TASK_INTERRUPTIBLE);
+ set_current_state(TASK_IDLE);
/*
* By the time the rescuer is requested to stop, the workqueue
From fbf1c41fc0f4d3574ac2377245efd666c1fa3075 Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben@decadent.org.uk>
Date: Sun, 3 Sep 2017 01:18:41 +0100
Subject: [PATCH 4/4] workqueue: Fix flag collision
Commit 0a94efb5acbb ("workqueue: implicit ordered attribute should be
overridable") introduced a __WQ_ORDERED_EXPLICIT flag but gave it the
same value as __WQ_LEGACY. I don't believe these were intended to
mean the same thing, so renumber __WQ_ORDERED_EXPLICIT.
Fixes: 0a94efb5acbb ("workqueue: implicit ordered attribute should be ...")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: stable@vger.kernel.org # v4.13
Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/workqueue.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index db6dc9dc0482..1c49431f3121 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -323,8 +323,8 @@ enum {
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
__WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
- __WQ_ORDERED_EXPLICIT = 1 << 18, /* internal: alloc_ordered_workqueue() */
__WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */
+ __WQ_ORDERED_EXPLICIT = 1 << 19, /* internal: alloc_ordered_workqueue() */
WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */