[Novalug] Re: virtualization Now

Paul W. Frields stickster@gmail.com
Sun Jan 6 20:18:29 EST 2008


On Sun, 2008-01-06 at 19:49 -0500, Jay Hart wrote:
> This is what I get as a result of reading /proc/cpuinfo.  Does this mean I
> lack support for virtualization?
[...snip of 'cat /proc/cpuinfo'...]
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
> pat pse36 mmx fxsr sse syscall mmxext 3dnowext 3dnow up ts

If you don't see "vmx" (Intel) or "svm" (AMD) your CPU doesn't support
*hardware* virtualization.  That doesn't mean you can't run VMs, just
that you will not get the benefit of hardware acceleration.  On some
motherboards you may need to make sure your BIOS also has the hardware
virt enabled, because it is possible for your CPU to support hardware
virt -- it will still show the flag in /proc/cpuinfo -- while the
motherboard has the capability disabled.  This also implies that you
can't just swap in a hardware virt-capable CPU onto any old motherboard
and get an immediate benefit.

If you use Xen "paravirtualized" guests -- where the host kernel and the
guest kernel have special hooks compiled in -- you won't notice too big
a difference.  These types of guests run at nearly native speed, are
quite pleasant to use, and are how virtualization got its start.  (Some
hosting companies did this before there was ever hardware virtualization
in CPUs.)

Running OSes without the availability of these special hooks requires
"full virtualization."  If you want to run a Windows XP guest -- where
you have no option to change the kernel, yay proprietary OSes! -- it
will probably be quite slow... from noticeable to unbearable depending
on your expectations.  VMWare gets around this problem with some slick
(and unfortunately proprietary) kernel modules and guest-domain tools,
but with newer CPUs people can get great results from FOSS stacks.  With
hardware virt capability, you can run a fully virtualized Windows XP
guest at near-native speed on top of FOSS software, which helps for
those pesky situations (like corporate requirements) where you need to
have a proprietary OS at hand.

-- 
Paul W. Frields, RHCE                          http://paul.frields.org/
  gpg fingerprint: 3DA6 A0AC 6D58 FEC4 0233  5906 ACDB C937 BD11 3717
           Fedora Project: http://pfrields.fedorapeople.org/
  irc.freenode.net: stickster @ #fedora-docs, #fedora-devel, #fredlug
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