Re: xen bootcamp (was: xen: was Challenge to you: Voice your concerns regarding systemd) upstream
On Wed, 1 Oct 2014 12:20:31 +0400
Reco <recoverym4n@gmail.com> wrote:
> Hi.
Hi Reco,
This is outstanding information. Thank you!
>
> On Tue, Sep 30, 2014 at 04:16:41PM -0400, Steve Litt wrote:
> > On Tue, 30 Sep 2014 17:57:41 +0400
> > Reco <recoverym4n@gmail.com> wrote:
> >
> > > Ok, ok. We all got it already. S*stemd in Debian = bad. S*stemd in
> > > Fedora = good. Fedora has no xen, hence = bad. Debian has xen,
> > > hence = good.
[snip history of xen]
>
> Xen is a microkernel, and there's two major versions of such
> microkernel
> - 3 and 4. Debian currently uses version 4, about the only one who
> uses version 3 today is Oracle. Xen's microkernel is a free software.
>
> But there's more to that as there's Xen's API made for controlling
> domUs, in fact, there's two sets of Xen's API - xm (made by human
> beings for human begins), and its successor xl (made by our friends
> from Mars for robots). Again, Xen's API is a free software.
>
> But using Xen's API directly is not the thing that Joe the average
> admin would do. Hence, there're tools which use Xen's API:
>
> - venerable xm toolset
> - hipster xl toolset
> - RedHat's pet libvirt
> - that thingie they put into XenServer
> - an abomination they put into OracleVM
> - that secret thing they in at Amazon
>
> Hence a choice of distribution depends on a Xen toolset of choosing
> and a huge portion of a personal taste.
So what do you think of the toolset that comes with Debian?
Hypothetically, if you were a person who hated the concept of systemd,
in the case of using Debian for dom0 and dom0 only, with no X, would
you care whether or not the dom0 initted from systemd? At that point,
isn't the Linux distro just a well-segregated piece of xen dom0?
>
>
> > To my way of thinking, the dom0 OS isn't really being used as an OS
> > at all: It's just an enabler for xen, and to my way of thinking,
> > that means it has way fewer challenges than a normal OS. So if it
> > uses systemd, so what? It's not like you have to worry about
> > running Gimp or Gnome or KDE or various authentication facilities
> > directly on it: It's a vehicle for xen, no more, no less.
>
> On a typical virtualization server - yes, dom0 is used for managing
> domUs, and not much more.
>
> But, if you need to run X - things are very different, as you use dom0
> as a conventional PC. Because - it's *very* difficult to force Xen to
> transfer control of your video card to domU. Possible, but very
> difficult, and hardware specific.
All I know of xen is what I've overheard in discussions and seen in
that one guy's presentation, but my impression was that the way to use
xen is to have xen on a server and access its domU guest OS's on a
client machine. Is that true?
>
>
> > I went to a Xen talk, and as I remember the guy said Xen is
> > developed and tested on Ubuntu, so that's your best bet. Yeah,
> > Ubuntu will have systemd, but if it works for the xen people, it
> > should work for us all.
>
> That guy does not seem to know what he's talking about. Xen is
> developed by Xen Project (xen.org), Citrix and Oracle (they like to
> say so, at least). Ubuntu merely builds Xen from the source, as
> others do.
I probably heard wrong or interpreted wrong. The guy seemed very
knowledgeable, not just to me, but to the other hundred or so people in
the room who were asking lots of questions. It's probable I just got
confused.
[snip netBSD stuff]
>
> > Unless I'm vastly misinformed, once your dom0 xen is installed, you
> > can now install domU hosts of any type you want, with or without
> > systemd, and use them to your heart's content.
> >
> > Am I understanding the situation right?
>
> Yes, that's correct. To run so called 'fully virtualized OS' (i.e. not
> modified to work with Xen) you'll need to have Intel VT-d CPU flag (or
> an appropriate AMD equivalent), but that's all that required.
Isn't that VM support built into all desktop mobo/CPU systems built in
the last 3 years?
> Convincing domU to use a real hardware is entirely different story.
Personally, I wouldn't want to use real hardware, for much the same
reason as my objections to systemd: Modularity. If I'm going to use xen
as a layer beneath my (perceived) OS, I want all my calls to go to that
layer, not the hardware beneath it. Unless, of course, there's a huge
performance advantage kind of like the DOS days when you wrote to B800
instead of using the BIOS write to screen, in order to speed up screen
write by a factor of five or ten. But my understanding is that if the
machine with dom0 has VM speedup built into the CPU/mobo, it goes fast
enough.
Just one more question: What's your opinion of Debian as a vehicle to
deploy a xen dom0?
Thanks,
SteveT
Steve Litt * http://www.troubleshooters.com/
Troubleshooting Training * Human Performance
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