[ 011/108] workqueue: reimplement work_on_cpu() using system_wq

Ben Hutchings
2012-10-07T23:22:21Z

From: Tejun Heo <tj@kernel.org>

commit ed48ece27cd3d5ee0354c32bbaec0f3e1d4715c3 upstream.

The existing work_on_cpu() implementation is hugely inefficient. It
creates a new kthread, execute that single function and then let the
kthread die on each invocation.

Now that system_wq can handle concurrent executions, there's no
advantage of doing this. Reimplement work_on_cpu() using system_wq
which makes it simpler and way more efficient.

stable: While this isn't a fix in itself, it's needed to fix a
workqueue related bug in cpufreq/powernow-k8. AFAICS, this
shouldn't break other existing users.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/workqueue.c | 25 ++++++++-----------------
1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b80065a..3c5a79e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3576,18 +3576,17 @@ static int __devinit workqueue_cpu_down_callback(struct notifier_block *nfb,
#ifdef CONFIG_SMP

struct work_for_cpu {
- struct completion completion;
+ struct work_struct work;
long (*fn)(void *);
void *arg;
long ret;
};

-static int do_work_for_cpu(void *_wfc)
+static void work_for_cpu_fn(struct work_struct *work)
{
- struct work_for_cpu *wfc = _wfc;
+ struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);
+
wfc->ret = wfc->fn(wfc->arg);
- complete(&wfc->completion);
- return 0;
}

/**
@@ -3602,19 +3601,11 @@ static int do_work_for_cpu(void *_wfc)
*/
long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
{
- struct task_struct *sub_thread;
- struct work_for_cpu wfc = {
- .completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
- .fn = fn,
- .arg = arg,
- };
+ struct work_for_cpu wfc = { .fn = fn, .arg = arg };

- sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
- if (IS_ERR(sub_thread))
- return PTR_ERR(sub_thread);
- kthread_bind(sub_thread, cpu);
- wake_up_process(sub_thread);
- wait_for_completion(&wfc.completion);
+ INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
+ schedule_work_on(cpu, &wfc.work);
+ flush_work(&wfc.work);
return wfc.ret;
}
EXPORT_SYMBOL_GPL(work_on_cpu);