Re: PCI serial?

[Gregory Nowak <greg@romuald.net.eu.org>]

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On Sat, Jul 28, 2007 at 11:38:40AM -0700, Zachary Kline wrote:
> I'm not too sure about the performance hit of using a VM vs 
> using a physical machine, but it doesn't seem that bad.  New kernels compile 
> fine, anyways.

Well, I can only speak from my own experience here obviously. This
will of course depend on your hardware, as well as the vm software you
use. I stand to be corrected here, but I think the main key here is
how many instructions get executed by the physical cpu vs how many get
emulated by the vm/how much code recompiling the vm needs to do on the
fly to execute the modified code on the physical cpu.

For example, I'm running virtualbox, and virtualpc on a 1.1GHz
celeron, with 512Mb of physical ram. I've run both gnu/linux as a
guest, as well as winxp temporarily for testing purposes. From my
perspective, both run about the same under virtualbox, as they do on
the host. In fact, the only way I can remember I'm in the guest, and
not actually on the host, is that there is a very slight delay between
pressing a key on the keyboard, and the action resulting in the key
press. This delay of course doesn't exist on the physical machine, and
is barely noticeable on the guest as it is. It's certainly not long
enough to be annoying, although I guess it may be annoying just a bit
if you're typing fast with key echo, and are sensitive to how fast you
hear the character you just typed. My guess is that if I had something
more modern, say a 2GHz dual-core system, this delay might not even
exist, or at least not be noticeable.

I also do find that when using gnu/linux as the guest, and
espeak/speechd-up/speech-dispatcher for software speech, if I'm
typing, or reading character by character, there is a slight barely
perceptible echo of the last half-a-second of text spoken at the
end. Since this doesn't however happen when running window-eyes under
winxp as the guest, I think this may be due to how
alsa/espeak/something else deals with the emulated sound hardware.

On the other hand, when running virtualpc under the same physical
hardware, the performance of the vm is noticeably slower, in my humble
opinion, even if the
guest additions are installed in a windows guest. My biggest issue
overall running a vm on this system is the amount of ram I'm able to
allocate to the guest, though this wouldn't be a problem most likely on
a more modern system. Hth.

Greg


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