Re: LuaJIT-on-Xen?
- From: Alexander Gladysh <agladysh@xxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Sun, 5 May 2013 16:00:16 +0400
On Sun, May 5, 2013 at 9:19 AM, Javier Guerra Giraldez
<javier@xxxxxxxxxxx> wrote:
> On Sat, May 4, 2013 at 11:54 PM, Alexander Gladysh <agladysh@xxxxxxxxx> wrote:
>>> Xen itself (as of a few years ago) is pretty well documented in "The
>>> Definitive Guide to the Xen Hypervisor". But it's not clear to me that
>>> there are advantages to Xen as a hypervisor relative to, say, kvm or
>>> even LXC.
>>
>> Well, Xen vs. kvm is debatable, but, AFAIK, LXC does not allow any
>> meaningful resource management, and reuses the host kernel. We had
>> this with OpenVZ years ago, and that was quite enough..
>
> LXC "containers" are quite nice. they all use the same kernel, so
> there's no "extra" virtualization overhead. you can limit CPU,
> network bandwidth, IO, RAM, etc, you can suspend, freeze, save,
> restore, migrate... it basically does everything Virtuozzo did ages
> ago (and OpenVZ after that). I think the administration tools are not
> so polished, but now it's fully supported from libvirt and OpenStack.
I mean that we were *not* happy with the level of isolation that
OpenVZ provided (several years ago).
Are there any texts documenting experience with LXC under high load
scenarios? I'm especially interested in rationing HDD between several
VMs (containers?), including a few very aggressive HDD users.
In our experience, this is somewhat problematic even for Xen (but it
is possible that we don't wield it good enough).
> in fact, this project would be almost trivial with LXC, since a
> container starts with an arbitrary process that becomes the root of
> the subtee, and looks like PID#1 "from inside". if that process is
> "init", and you give it a full installation in the chroot, then you
> have a new OS in a VM. if it's any other proces (say, a LuaJIT
> worker!) then it's a lot simpler, like a better chroot
Well, yes. But will the isolation be good enough?
We hit many kinds of pitfalls with Xen (and with OpenVZ earlier), so
I'm wary about adopting yet another virtualization scheme... That
being said, we're already using LXC at a very basic level (mostly in
development / testing scenarios where we need to emulate Xen cluster
without paying the full cost), and plan to use it more, so it is not
*that* alien and unknown. :-)
>>> If you're stuck on a Xen host, of course, yes, it would be
>>> nice to be able to toss the OS in the DomU out and get down to "bare
>>> metal" Xen.
>>
>> Are you suggesting that it will be easier with, say, kvm?
>
> I don't think so. kvm doesn't have a 'paravirtualization' flavor, so
> everything looks like hardware. even virtio (the generic interface
> below the "paravirtualized drivers") is presented like a PCI hardware.
> Xen syscalls are slightly higher level.
OK, I see.
Thanks,
Alexander.
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