linux-kernel - Re: [RFC][PATCH v8 1/2] printk: Make printk() completely async

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Date:	Tue, 5 Apr 2016 02:01:05 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Jan Kara <jack@...e.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>, Tejun Heo <tj@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org,
	Byungchul Park <byungchul.park@....com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCH v8 1/2] printk: Make printk() completely async

Hello,

On (04/04/16 11:41), Petr Mladek wrote:
[..]
> > So what about having printk_kthread_func() like:
> > 
> > 	while (1) {
> > 		set_current_state(TASK_INTERRUPTIBLE);
> > 		if (!need_flush_console)
> > 			schedule();
> > 		__set_current_state(TASK_RUNNING);
> > 		need_flush_console = false;
> > 		console_lock();
> > 		console_unlock();
> > 	}
> > 
> > In vprintk_emit() we do:
> > 
> > 	if (!in_panic && printk_kthread) {
> > 		/* Offload printing to a schedulable context. */
> > 		need_flush_console = true;
> > 		wake_up_process(printk_kthread);
> > 	} else {
> > 		...
> > 
> > This guarantees that after message was appended to the buffer in
> > vprintk_emit(), the message got either printed by console_unlock() or
> > printk_kthread is in TASK_RUNNING state and will call console_unlock() once
> > scheduled. It also guarantees that printk_kthread_func() won't loop forever
> > when there's nothing to print. And that is all we need...
> > 
> > I think the simplicity of this is worth the possible extra loops in
> > printk_kthread_func().
> 
> I do not have strong opinion about this. I agree that the simplicity
> of your proposal is nice. You are much more experienced kernel
> developer. If you say that the potential extra loop is fine, I am
> fine with it as well :-)
> 

works for me, re-sent.
the patch is even smaller now, and we almost have nothing else to
cut off from it :)

	-ss