On Jul 25, 2008, at 8:48 AM, McKown, John wrote:
Somewhat like BOCH? I remember somebody saying that they ran Windows
on
BOCH on an old P/390.
A little more data: the straight-up portable-emulation x86 code-path
is still not a good idea. I got the current released bochs (20080720)
built (with all the cool stuff like x86_64, SSE, plenty of neat
features) on Linux s390x. The build was quite clean, actually.
It is a lot less painful than on a P/390 or H70, but running Bochs on
a 2094 (z9 of some sort), where z/VM sees 2 CPUs but the Linux guest
has one, is still only giving me 3.4 to 4.0 million (x86) instructions
per second, which is...well, a LOT less than you'd get on a modern
Xeon. That's not to say that I'm necessarily CPU-bound. If I had
time to play with it, the VGA refresh rate is where I'd start, because
that probably isn't helping.
FreeDOS installation was pokey but not really terrible. Performance
is, well pretty bad; it feels like working over a satellite link in
terms of latency. I think you'd have a really hard time making the
case to management that THIS was a good use for your zSeries.
So here's hoping that the Mantissa product is focussed around an
efficient (and almost-certainly assembly) x86 emulation. Given the
richness of the s390x instruction set, and that a bunch of the
instructions fundamentally do the same thing in the x86 and the s390x
world (that is, "move something from a memory location to a named
register" is the same concept on either architecture), I would hope
that most of the user-mode instructions can be mapped close to 1-to-1,
and the mere fact of having to create an instruction translator is
going to mean that the actual performance will be several-host-
instructions-to-one-guest-instruction. Complicated instructions are
still going to be slowed significantly, of course.
Adam
