linux-kernel - Re: [patch 0/3] kvm tool: Serial emulation overhaul

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Date:	Mon, 12 Dec 2011 10:27:50 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Sasha Levin <levinsasha928@...il.com>
Subject: Re: [patch 0/3] kvm tool: Serial emulation overhaul

> Well, the difference between ssh and serial is, that ssh can pack 1.5k
> worth of data into one frame, while serial has to send it
> piecewise. And the emulation has to trap into kvm tool for each tx
> byte, which doesnt help either. We cannot do much with buffering on
> the kvm tool side as we have no clue how much consecutive data will
> come in. That's why there is a virtual console, which has the
> disadvantage that you cant see the early boot messages.

You can emulate a chip with a 64byte or so FIFO. You can do I/O cycle
prediction in the kernel part and you can use the empty bit as a clue
(which is what most serial<->ethernet widgetry does).

Alan
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