workqueue: implement unbound workqueue
This patch implements unbound workqueue which can be specified with
WQ_UNBOUND flag on creation. An unbound workqueue has the following
properties.
* It uses a dedicated gcwq with a pseudo CPU number WORK_CPU_UNBOUND.
This gcwq is always online and disassociated.
* Workers are not bound to any CPU and not concurrency managed. Works
are dispatched to workers as soon as possible and the only applied
limitation is @max_active. IOW, all unbound workqeueues are
implicitly high priority.
Unbound workqueues can be used as simple execution context provider.
Contexts unbound to any cpu are served as soon as possible.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: David Howells <dhowells@redhat.com>
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 139069a..67ce734 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -51,7 +51,8 @@
WORK_NO_COLOR = WORK_NR_COLORS,
/* special cpu IDs */
- WORK_CPU_NONE = NR_CPUS,
+ WORK_CPU_UNBOUND = NR_CPUS,
+ WORK_CPU_NONE = NR_CPUS + 1,
WORK_CPU_LAST = WORK_CPU_NONE,
/*
@@ -237,11 +238,17 @@
WQ_RESCUER = 1 << 3, /* has an rescue worker */
WQ_HIGHPRI = 1 << 4, /* high priority */
WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */
+ WQ_UNBOUND = 1 << 6, /* not bound to any cpu */
WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
+ WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2,
};
+/* unbound wq's aren't per-cpu, scale max_active according to #cpus */
+#define WQ_UNBOUND_MAX_ACTIVE \
+ max_t(int, WQ_MAX_ACTIVE, num_possible_cpus() * WQ_MAX_UNBOUND_PER_CPU)
+
/*
* System-wide workqueues which are always present.
*
@@ -256,10 +263,16 @@
* system_nrt_wq is non-reentrant and guarantees that any given work
* item is never executed in parallel by multiple CPUs. Queue
* flushing might take relatively long.
+ *
+ * system_unbound_wq is unbound workqueue. Workers are not bound to
+ * any specific CPU, not concurrency managed, and all queued works are
+ * executed immediately as long as max_active limit is not reached and
+ * resources are available.
*/
extern struct workqueue_struct *system_wq;
extern struct workqueue_struct *system_long_wq;
extern struct workqueue_struct *system_nrt_wq;
+extern struct workqueue_struct *system_unbound_wq;
extern struct workqueue_struct *
__alloc_workqueue_key(const char *name, unsigned int flags, int max_active,