workqueue: Add new WQ_PERCPU flag
Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.
This lack of consistentcy cannot be addressed without refactoring the API.
This patch adds a new WQ_PERCPU flag to explicitly request the use of
the per-CPU behavior. Both flags coexist for one release cycle to allow
callers to transition their calls.
Once migration is complete, WQ_UNBOUND can be removed and unbound will
become the implicit default.
tj: Merged doc patch.
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index e295835..165ca73 100644
--- a/Documentation/core-api/workqueue.rst
+++ b/Documentation/core-api/workqueue.rst
@@ -183,6 +183,12 @@
BH work items cannot sleep. All other features such as delayed queueing,
flushing and canceling are supported.
+``WQ_PERCPU``
+ Work items queued to a per-cpu wq are bound to a specific CPU.
+ This flag is the right choice when cpu locality is important.
+
+ This flag is the complement of ``WQ_UNBOUND``.
+
``WQ_UNBOUND``
Work items queued to an unbound wq are served by the special
worker-pools which host workers which are not bound to any
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 74b0042..f190726 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -401,6 +401,7 @@ enum wq_flags {
* http://thread.gmane.org/gmane.linux.kernel/1480396
*/
WQ_POWER_EFFICIENT = 1 << 7,
+ WQ_PERCPU = 1 << 8, /* bound to a specific cpu */
__WQ_DESTROYING = 1 << 15, /* internal: workqueue is destroying */
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
