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Date: Mon, 12 Dec 2011 11:02:36 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
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Subject: Re: [patch 0/3] kvm tool: Serial emulation overhaul
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> > 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 ?