

QEMU 1.7.0 is now available - conductor
https://lists.gnu.org/archive/html/qemu-devel/2013-12/msg01770.html

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apetresc
Can someone explain in technical-but-not-necessarily-domain-expert terms what
the relationship between QEMU and KVM is? Is one a dependency of the other, or
could they each work independent of the other?

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djfergus
KVM (Kernel Virtual Machine) is a Linux kernel module that allows a user space
program to utilize the hardware virtualization features of various processors.

QEMU is a machine emulator.

QEMU can make use of KVM when running a target architecture that is the same
as the host architecture (which gives significant performance advantages).

KVM is not strictly dependent on QEMU but they are usually used together. If
you don't need the kernel level hw support (i.e. emulating a different
architecture to the host platform) then QEMU can be used independently.

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apetresc
Thank you, that's pretty much perfect :)

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jevinskie
I'd like to hear stories about people using QEMU in production. Do people
think it is a viable option for automated ARM Android testing?

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devicenull
Er, what? QEMU is used very frequently with KVM. There are many companies
providing KVM instances, so QEMU is pretty widely used in production. Did you
have a more specific question?

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wtallis
Xen also uses QEMU, in pretty much the same manner as KVM.

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bonzini
That's not entirely true. Xen uses QEMU only to execute I/O. It gets I/O
requests on a ring buffer and services them. CPUs are handled by the
hypervisor.

With KVM, QEMU actually runs the code for the virtual machine; it just does
that inside the KVM kernel module.

This means, for example, that only with KVM you can profile each VCPU simply
using "perf". Also, features that require code to run in the CPU threads (for
example slowing down CPUs so that migration can converge better) will not work
with Xen.

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gwu78
Let me know when we can compile QEMU with a modest amount of RAM. Last time I
tried, on a memory constrained laptop, it took over 1GB of RAM! That's a lot
of memory just to compile a single program. By comparison, I can compile a
kernel loaded down with heaps of unneeded drivers with less than 200MB of RAM.
I suspect this situation will only get worse with future QEMU releases.

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stefanha
Try again with QEMU 1.7 and recent gcc. There has been a known gcc issue
triggered by one of the QEMU source files that requires a lot of memory. A
workaround went into QEMU a while back using the gcc -fno-gcse flag for that
particular source file.

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steeve
Does anyone know if QEMU can do virtualization on hosts other than Linux (via
KVM)? I'd love to ditch Virtualbox for it.

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seryoiupfurds
I've used Qemu on Windows and OpenBSD. I don't think either supports KVM
acceleration though.

