linux-kernel - Re: [RFC][PATCHv2 8/8] printk: enable printk offloading

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Message-ID: <20170403154210.GG3452@pathway.suse.cz>
Date:   Mon, 3 Apr 2017 17:42:10 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Len Brown <len.brown@...el.com>, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv2 8/8] printk: enable printk offloading

On Wed 2017-03-29 18:25:11, Sergey Senozhatsky wrote:
> Initialize the kernel printing thread and enable printk()
> offloading.
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> ---
>  kernel/printk/printk.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 0d96839bb450..acfdc50580db 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2796,6 +2796,25 @@ static int printk_kthread_func(void *data)
>  	return 0;
>  }
>  
> +/*
> + * Init printk kthread at late_initcall stage, after core/arch/device/etc.
> + * initialization.
> + */
> +static int __init init_printk_kthread(void)
> +{
> +	struct task_struct *thread;
> +
> +	thread = kthread_run(printk_kthread_func, NULL, "printk");
> +	if (IS_ERR(thread)) {
> +		pr_err("printk: unable to create printing thread\n");
> +		return PTR_ERR(thread);
> +	}
> +
> +	printk_kthread = thread;
> +	return 0;
> +}
> +late_initcall(init_printk_kthread);

I like the simplicity. I just wonder if people on tiny devices might
want to disable it. In each case, it does not make sense on non-SMP
machines or when people force the emergency mode all the time.

I am not sure what is the practice here. I wonder if we should be
proactive or keep it as is and wait until anyone complains. IMHO,
it is not that big deal but...

Best Regards,
Petr