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Commit ed48ece2 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: reimplement work_on_cpu() using system_wq 



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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarJiri 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>
Cc: stable@vger.kernel.org
parent 960bd11b

kernel/workqueue.c

+8 −17
Original line number Diff line number Diff line
@@ -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);