linux-kernel - Re: [PATCH] workqueue: reimplement work_on_cpu() using system

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Date:	Wed, 19 Sep 2012 13:32:14 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Len Brown <lenb@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] workqueue: reimplement work_on_cpu() using system_wq

On Tue, 18 Sep 2012, Tejun Heo wrote:

> >From 760824d48d8a1f302b80367681ada19836d93521 Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Tue, 18 Sep 2012 12:48:43 -0700
> 
> 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.

Makes sense. I have tested that after dropping your conversion of APM 
on_cpu0() and using this one instead, everything works.

> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Jiri Kosina <jkosina@...e.cz>

Acked-by: Jiri Kosina <jkosina@...e.cz>

> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Len Brown <lenb@...nel.org>
> Cc: Rafael J. Wysocki <rjw@...k.pl>
> ---
> Applying to wq/for-3.7.
> 
> Thanks.
> 
>  kernel/workqueue.c |   25 ++++++++-----------------
>  1 files changed, 8 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 3e324aa..737ab01 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3624,18 +3624,17 @@ static int __cpuinit 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;
>  }
>  
>  /**
> @@ -3650,19 +3649,11 @@ 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);
> -- 
> 1.7.7.3
> 

-- 
Jiri Kosina
SUSE Labs
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