[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Xen-devel] Re: [Devel] Re: [RFC] Virtualization steps

Kirill Korotaev wrote:
Oh, after you come to an agreement and start posting patches, can you
also outline why we want this in the kernel (what it does that low
level virtualization doesn't, etc, etc), and how and why you've agreed
to implement it. Basically, some background and a summary of your
discussions for those who can't follow everything. Or is that a faq
Nick, will be glad to shed some light on it.

First of all, what it does which low level virtualization can't:
- it allows to run 100 containers on 1GB RAM
  (it is called containers, VE - Virtual Environments,
   VPS - Virtual Private Servers).
- it has no much overhead (<1-2%), which is unavoidable with hardware
  virtualization. For example, Xen has >20% overhead on disk I/O.

I think the Xen guys would disagree with you on this. Xen claims <3% overhead on the XenSource site.

Where did you get these figures from? What Xen version did you test? What was your configuration? Did you have kernel debugging enabled? You can't just post numbers without the data to back it up, especially when it conflicts greatly with the Xen developers statements. AFAIK Xen is well on it's way to inclusion into the mainstream kernel.
I have no exact numbers in the hands as I'm in another country right now.
But! We tested Xen not long ago with iozone test suite and it gave ~20-30% disk I/O overhead. Recently we were testing CPU scheduler and EDF scheduler gave me 33% overhead on some very simple loads with almost busy loops inside VMs. It also was not providing any good fairness on 2CPU SMP system to my suprise. You can object to me, but better simply retest it if interested yourself. There were other tests as well, which reported very different overheads on Xen 3. I suppose Xen guys do such measurements themself, no? And I'm sure, they are constantly improving it, they are doing a good work on it.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.