workqueue: use hotcpu_notifier() for workqueue_cpu_down_callback()
workqueue_cpu_down_callback() is used only if HOTPLUG_CPU=y, so
hotcpu_notifier() fits better than cpu_notifier().
When HOTPLUG_CPU=y, hotcpu_notifier() and cpu_notifier() are the same.
When HOTPLUG_CPU=n, if we use cpu_notifier(),
workqueue_cpu_down_callback() will be called during boot to do
nothing, and the memory of workqueue_cpu_down_callback() and
gcwq_unbind_fn() will be discarded after boot.
If we use hotcpu_notifier(), we can avoid the no-op call of
workqueue_cpu_down_callback() and the memory of
workqueue_cpu_down_callback() and gcwq_unbind_fn() will be discard at
build time:
$ ls -l kernel/workqueue.o.cpu_notifier kernel/workqueue.o.hotcpu_notifier
-rw-rw-r-- 1 laijs laijs 484080 Sep 15 11:31 kernel/workqueue.o.cpu_notifier
-rw-rw-r-- 1 laijs laijs 478240 Sep 15 11:31 kernel/workqueue.o.hotcpu_notifier
$ size kernel/workqueue.o.cpu_notifier kernel/workqueue.o.hotcpu_notifier
text data bss dec hex filename
18513 2387 1221 22121 5669 kernel/workqueue.o.cpu_notifier
18082 2355 1221 21658 549a kernel/workqueue.o.hotcpu_notifier
tj: Updated description.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 942bb75..48becab 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3807,7 +3807,7 @@
WORK_CPU_LAST);
cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_UP);
- cpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);
+ hotcpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);
/* initialize gcwqs */
for_each_gcwq_cpu(cpu) {