linux-kernel - Re: [RFC][PATCH 7/7] serial, 8250: Mostly avoid wakeups from under port->lock

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Message-ID: <20111221185112.47a4c1ad@pyramind.ukuu.org.uk>
Date:	Wed, 21 Dec 2011 18:51:12 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Ted Ts'o" <tytso@....edu>, Greg KH <greg@...ah.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	akpm@...ux-foundation.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 7/7] serial, 8250: Mostly avoid wakeups from under
 port->lock

> > Also I think it's probably buggy - sending the x_char is forward progress
> > so probably needs to cause a wakeup.
> 
> Could you explain that more, its not actually connecting with any
> neurons..

The tty output queue is the ring buffer + one byte (x_char). It's
effectively two priority queues one of which is 1 byte long and high
priority, the other of which is low priority.

> > So for the moment NAK, but worthy of figuring out how to do it right
> 
> OK, will try and see if I can poke at it a level upwards.. 

I think that is the right magic - and also means all the embedded
consoles might be poked the right way.
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