Comparing Linux huge memory pages & Kernel Samepage Merging for KVM virtualization

A quick test (so take it with a grain of salt):

  1. Huge pages is slightly faster than not using huge pages (~10% with 4 winxp virtual machines copying 512MB from one memory location to another).
  2. KSM is slightly slower then not using KSM (~5% with 4 winxp virtual machines copying 512MB from one memory location to another).

So, at first glance it would appear that we can use a loose rule of thumb:

  1. to consolidate the maximum number of machines, use KSM as it will allow you to over commit the amount of memory on your box.
    1. Risk: if the memory pages are significantly different, you may start swapping in a very bad way. This is where monitoring comes in
  2. to give the best performance to a number of machines, use huge memory pages.. does not allow you to over commit
    1. Risk: if you don’t leave enough memory for the host os, you can crash your machine. This is also where monitoring comes in
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Proxmox VE 1.8 and KVM: Adding sound to your virtual machines!

This assumes that your host machine has a sound card! 🙂

Add the args line in your /etc/qemu-server/<vm id>.conf file should give you sound:

args: -soundhw

On my Proxmox VE 1.8, I have several virtual audio devices available.   I’ve had the best luck with ac97 with Windows XP/Vista and Win7.

red:/etc/qemu-server# kvm -soundhw ‘?’
Valid sound card names (comma separated):
pcspk       PC speaker
sb16        Creative Sound Blaster 16
ac97        Intel 82801AA AC97 Audio
es1370      ENSONIQ AudioPCI ES1370
hda         Intel HD Audio

-soundhw all will enable all of the above

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