RFC: Primary architecture promotion requirements

[Richard W.M. Jones]

On Wed, Mar 21, 2012 at 01:11:27PM -0500, Dennis Gilmore wrote:
> I have spoken with the OpenSUSE guys they dont use qemu-system-arm but
> rather qemu-arm and lay out things and build using a hybrid
> environment  thats also how they build ppc s390 and other arches. the
> only build hardware they have is x86. doing full system emulation will
> be slower. 

In case it's not clear to the peanut gallery, qemu-system-arm and
qemu-arm work in different ways. 

qemu-system-arm emulates a complete machine, so your ARM kernel is
also running and being emulated.  qemu-arm just emulates the userspace
part of the program, but translates system calls from the program and
runs them against the regular (x86-64 in this case) kernel.

qemu-arm should be a lot faster, since the kernel part is running at
full speed.  On the other hand, there's some start-up overhead for
every process run this way.

I should also say that in both cases qemu's "TCG" emulation is
reasonably smart, and recompiles guest ARM code on the fly down to
native (x86-64 in this case) code.  Recommended reading:
http://lugatgt.org/content/qemu_internals/downloads/slides.pdf

Rich.

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Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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