On 3/16/07, Alan Altmark <[EMAIL PROTECTED]> wrote:
Sir, let's not throw the baby out with the bathwater, eh? There are all sorts of places where the underlying hardware does *not* shine through to the guest. Example: the integrated 3270 console. VM continues to run under VM just fine, albeit at a lower level of "awareness" of its surroundings.
I did not mean to say that imperfect virtualization is bad. It's an obvious trade-off and in most cases goodness because for virtualization to make sense you do not want to be bothered with the obligations that come with having all the bits in place. Virtualization works because you *can* abstract from details. What I tried to explain is that in-band controls means that CP takes part of the resources for itself, and hands out the rest to the guests. With out-of-band controls CP requires some other technology (outside the architecture) that it does not virtualize for a guest. At that point you're unable to stack. And the built-in 3270 that you bring up is indeed one of those, because CP does not virtualize it for the guest (unlike the line mode system console with VINPUT and friends). Fortunately we don't need that to be virtualized to run VM because we have something else that works. Rob
