Re: [Qemu-devel] QEMU_TMPDIR temp folder for KQEMU for Windows.

[John R. Hogerhuis]

On Mon, 2005-08-29 at 11:05 -0700, Francois Rioux wrote:

> I notice that QEMU is quite slower than VMWare.

It certainly is.

>   Apparently due to the way IO occur.  What are the strategies to
> enhance that performance?

Curious, why do you think that? There are probably a whole host of
reasons that VmWare is faster, IO devices are only one part of the
picture.

The more interesting place for optimizations is on the dynamic code
generation. VmWare is a virtualizer while QEMU employs a default
strategy of dynamically generating direct (I think) threaded code. So
the way to achieve improved speed is to improve the dynamic code
generator.

KQEMU presumably does this on X86 by inlining more of the original code
with minimal changes (i.e more tokens containing bigger swaths of native
code, and less simple instruction emulation tokens), so performance will
be more like what you could expect from a virtualizer. KQEMU is not open
source though, so if you want to fiddle with that, you probably would
have to do it on qvm86.

As to IO, one thought is to run a Windows X server (such as the free one
that comes with Cygwin) natively on the host rather than under
emulation. Do testing with tuntap networking. User-net networking is
slow, Slirp code could certainly stand some bugfixes and optimizations.

There are different tricks you can do to improve the experience. For
example, avoid booting your virtual images from scratch. Boot to
desktop, and savevm. Then in the future, boot straight off the savevm,
it is much faster that way.

-- John.