linux-kernel - Re: [PATCH 8/8] printk: Add config option for disabling printk offloading

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Message-ID: <20140326172332.5f1e1bfb@alan.etchedpixels.co.uk>
Date:	Wed, 26 Mar 2014 17:23:32 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Jan Kara <jack@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, pmladek@...e.cz,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 8/8] printk: Add config option for disabling printk
 offloading

On Tue, 25 Mar 2014 18:55:01 +0100
Jan Kara <jack@...e.cz> wrote:

> Necessity for offloading of printing was observed only for large
> systems. So add a config option (disabled by default) which removes most
> of the overhead added by this functionality.

If its an option it'll not get used. It ought to be automatic.

I still think the mindset of this patch set is wrong. Only the device
driver really knows what is good or bad. A large x86 connected to a
network fake 16x50 serial port for example typically has a giant FIFO so
'bad' becomes 32K not 1000. A USB serial port already does async queueing
so the value is 0.

It also ignores priority so you might queue and loose an oops as a box
goes down in preference to reporting debugging crap.

All the afflicted consoles are serial, all go via the uart layer as far
as I can see.

The uart layer has a queue mechanism that could be used

Alan
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