linux-kernel - Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async

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Message-ID: <20160310095350.GP10940@pathway.suse.cz>
Date:	Thu, 10 Mar 2016 10:53:50 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Jan Kara <jack@...e.cz>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	akpm@...ux-foundation.org, jack@...e.com, tj@...nel.org,
	linux-kernel@...r.kernel.org, sergey.senozhatsky@...il.com
Subject: Re: [RFC][PATCH v2 1/2] printk: Make printk() completely async

On Wed 2016-03-09 15:09:50, Sergey Senozhatsky wrote:
> On (03/07/16 13:16), Jan Kara wrote:
> What do you think? Or would you prefer to first introduce async
> printk() rework, and move to console_unlock() in vprintk_emit()
> one release cycle later?
> IOW, in 3 steps:
> -- first make printk() async
> -- then console_unlock() async, and use console_unlock_for_printk() in
>    vprintk_emit()
>
> -- then switch to console_unlock() in vprintk_emit().

I would sort this by priorities. I know about real-world problems
that will get solved by async printk. I haven't heard yet people
complaining about blocked console_lock()/console_unlock() calls
outside printk code. So, I would personally prefer to handle
async printk first.

Heh, you opened an interesting can of worms. There are definitely
locations that just want to manipulate the list of consoles and
their setting without the need to push the date. I wonder how
many locations really need to push the data.

Note that console_unlock_for_printk() might be a bit
misleading. Especially when you suggest to replace it by
console_unlock() in vprintk_emit() ;-) I wonder if
console_flush_and_unlock() might be more descriptive.

We might even split flush_console() into a separate function in the end.
I think that the combination with unlock() is there to make sure
that somebody will flush the last messages from printk(), see
the retry stuff. It probably won't be needed with the asynch printk().

Anyway, all these console_unlock() changes looks like another big step
and I suggest to do it separately.

I looking forward to see where this ends.

Thanks,
Petr

PS: I want to check more precisely the async printk patchset but
I am repeatedy sidetracked this week :-(