QEMU: Just How Fast Is It?
It runs at 19% of host speed.
I last blogged about my experience with QEMU 71 days ago.
Since then I have brought up several other operating systems on it, including NT 4.0, Windows 2000 and FreeBSD 6.0. One thing I noticed is that the newer OSes has more demand on the system and therefore behaves more sluggishly, to the point of not being very useful.
My latest adventure with QEMU is a second try at Ubuntu 6.06 Beta (Dapper Drake).
Maybe it's because I have experienced Ubuntu once before, or maybe it's because Ubuntu 6.06 Beta is really that much better than 5.10, or maybe it's because I'm getting a little bit impatient with Fedora Core 5's degradations, my impression of Ubuntu has improved, even though it's running very slowly under QEMU.
To measure how much slower the emulated system is compared with the host system, I ran a little bench mark program that I found on the internet. The result can be found in the screenshot below:
The bench mark index is 294.0 on the host OS and 56.0 on the guest OS. So the guest is running at 19% of the speed of the host system, making my AMD64 3500+ look like a P3/700MHz.
Re: QEMU: Just How Fast Is It?
You might care to try Kqemu which is a kernel module that's supposed to accelerate QEMU's performance. QEMU automatically activates Kqemu support if the module is loaded.
One more thing, you shouldn't try testing any performance-related stuff on Fedora, it's not the fastest distro out there. Maybe Arch or Gentoo, or even SUPER, but certainly not Fedora.
Re: QEMU: Just How Fast Is It?
A combination of factors prevented me from using the kqemu kernel module for acceleration: there's no binary distributions of it for Fedora Core 5/x86_64 and it doesn't compile under GCC 4.0. I know I can build it but only after installing a substantial amount of compatibility packages.
I'm interested mainly on the relative numbers here. The other distributions do sound interesting. Maybe I'll try them out as QEMU guests. :) I'll let you know how many months it takes to emerge a Gentoo system under QEMU, after I figure out how to make kqemu work, of course.
Re: QEMU: Just How Fast Is It?
I guess qemu works with kvm from the latest 2.6.20 kernel as well. Applications run about %90 as fast as native. The benchmark I saw (google for kvn qemu kqemu) showed that kqemu was still a little faster but not by too much.
Qemu without kvm or kqemu will run very slow for sure. The HW will be %100 abstraced from the guest which is slow. The kvn and kqemu modules allow user space code to run non-emulated on the host CPU. This makes it run at %100 speed of course. Only the kernel space code is emulated thus protecting the host OS.
![[QEMU Full Virtualization Mode Performance]](http://www.weiqigao.com/blog/images/kqemu-debian-i386-performance.png){kind=link}