linux-kernel - Re: [PATCH] Use tty

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Message-ID: <464235F4.6080006@microgate.com>
Date:	Wed, 09 May 2007 14:58:28 -0600
From:	Paul Fulghum <paulkf@...rogate.com>
To:	James Simmons <jsimmons@...radead.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux console project <linuxconsole-dev@...ts.sourceforge.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Use tty_schedule in VT code.

Paul Fulghum wrote:
> As the tty flip buffer code has evolved, that delay value of 1
> was carried along. It may have had some historical purpose, but
> I can't figure it out and it appears to have no use currently.

I looked further back and in the 2.4 kernels this scheduling
was done with the timer task queue (process receive data on
next timer tick).

I guess the schedule_delayed_work() with a time delay of 1
was the best approximation of the previous behavior.

There is no logical reason to delay the first attempt at
processing receive data so schedule_delayed_work() in
tty_schedule_flip() should be changed to 0 (as was the
case for con_schedule_flip).

The schedule_delayed_work in flush_to_ldisc() will continue
to use a delay of 1 if the ldisc can't accept more data.
This allows the user app and ldisc to catch up.

Subsequent calls to tty_schedule_flip won't affect
this 'back off' delay because once the work is scheduled
(with a delay of 1) new scheduling calls are ignored for
the same work structure.

I've been testing the change to 0 in tty_schedule_flip()
under various loads and data rates with no ill effects.

-- 
Paul Fulghum
Microgate Systems, Ltd.
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