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

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Date:	Mon, 12 Dec 2011 20:21:46 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Sasha Levin <levinsasha928@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 0/3] kvm tool: Serial emulation overhaul

On 12/12/2011 01:02 PM, Alan Cox wrote:
> > > 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).
> > 
> > The performance problems here aren't the same performance problems you
> > have on real hardware. The problem here is that it costs 40k cycles for
> > the guest to access the emulated chip.
>
> How much of that 40K cycles is bouncing back and forth into emulation
> layers and how much of it is the kernel trap ?
>  

30K of those cycles are only in Sasha's mind, the real figure is 10K
(and likely lower with newer hardware).

-- 
error compiling committee.c: too many arguments to function

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