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acme (189)

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Leon Brocard (aka acme) is an orange-loving Perl eurohacker with many varied contributions to the Perl community, including the GraphViz module on the CPAN. YAPC::Europe was all his fault. He is still looking for a Perl Monger group he can start which begins with the letter 'D'.

Journal of acme (189)

Monday July 04, 2005
12:52 PM


[ #25509 ]
Looking back, I tend not to post about non-Perl geekery. This is clearly because I'm trying to impress you with all my Perl knowledge - what I don't know about Perl could, err, fit a big book. Moving quickly on, I've been playing with something which isn't Perl recently. I know, I know. In fact, most of it is quite low level and bits of it are in Python. I've been playing with the Xen virtual machine monitor.

Apart from sounding cool, it also does something quite useful. It allows one real computer to run multiple unreal (virtual) computers, which you can start, stop, pause and unpause. I reckon most software eventually reaches a level when it must be virtualised (clearly this is a stage after themes or sending mail), because the flexibility makes it so much more useful. Think of it as object indirection but for software packages.

While we hate software, it must also be remembered that software runs on hardware, and that it can be hateful too. Sometimes, hardware needs to be upgraded or fixed. Xen comes to the rescue by being able to save, restore and do live migration of virtual machines. Fab! No wonder systems people are excited about it. I've installed and played with it and I'm completely impressed (running Ubuntu under Ubuntu). I'm going to use it on my live systems. I'm going to use it to test software. I'm going to use it to, errr, do many things. It has two annoyances: migration requires a network file system (anyone built a good one yet?), and amd64 support isn't entirely there yet (those Opterons sure are shiny). Of course, user mode Linux does a similar thing, but check out the performance charts.

Looks like I'm a bit behind. gnat noticed xen in February and sky noticed a while ago too:

14:00 <acme> also, why didn't you tell me that xen was cool
14:00 <sky> I did
14:00 <acme> then why did i ignore you
14:00 <sky> I love xen
14:00 <sky> no idea
14:00 <acme> xen is cool
14:00 <sky> you suck
14:00 <sky> ;)

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  • "migration requires a network file system (anyone built a good one yet?)"

    There's v9fs [], though I haven't used it before.
  • One of the big disadvantages to solutions that provide a hardware monitor, like Xen or UML [] or VMWare or Bochs [] and of course complete system emulators like QEmu [], is that you lose a fair bit of speed in the overhead.

    Now, the vendor of Xen or whatever might come up with some over-simplified number to express the best performance they've seen for a conveniently chosen set of tasks, relative to applications running in the host system. "85% of host speed", they will shout. But the fact is that in addition to