RE: [Xen-users] Moved from Xen 2 to Xen 3... some questions..

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

George,

 

Steve Kemp kindly answered a few of your questions.

 

I'll try to answer some of the others, to the best of my abilities....

 

1. Was answered by Steve.

 

2. HVM support is automatically built into the kernel. So, as long as you have a processor that supports AMD SVM or Intels VMX technology, Xen will do what it needs to. LibVNCServer is needed by QEMU if you want to use VNC to view your virtual machine - you need EITHER VNC or SDL to see what's going on on a fully-virtualized machine - unless you want to connect to the virtual machine through some other networked means, of course - you can use SSH to connect to a Linux machine (or a Windows machine if you can find a SSH service to run on it), but that may not be what you WANT to do... And for debugging the boot process, it can be quite useful to see what's going on!

 

If it works, you'll see the Intel version of this:

(XEN) Initializing CPU#0
(XEN) Detected 2785.881 MHz processor.
(XEN) CPU0: AMD Flush Filter disabled
(XEN) CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
(XEN) CPU: L2 Cache: 1024K (64 bytes/line)
(XEN) CPU 0(2) -> Core 0
(XEN) AMD SVM Extension is enabled for cpu 0.
(XEN) Intel machine check architecture supported.
(XEN) Intel machine check reporting enabled on CPU#0.
(XEN) CPU0: AMD Athlon(tm) 64 FX-62 Dual Core Processor stepping 02

Where it says "AMD SVM Extension is enabled for cpu 0" it should say "Intel VMX Extension enabled" (or something very similar). If you don't see that in the boot messages, then you haven't got VMX enabled in the processor, and you need to do something to fix it.

 

3. I don't know if all BIOS has a option for this or not - I know one of our machines has the option the wrong way around - Set it to disabled and it works! If your BIOS doesn't do the right thing, you'd think by now that the latest BIOS for that motherboard would have the feature - unless it's so old that the manufacturer no longer updates the BIOS unless REALLY necessary of course... Since I work with AMD hardware, and my motherboards are all internal AMD prototypes, I can't really say for Intel products... See above to know if it works or not...

 

4. Yes, to be able to use a dual core processor, you should compile Xen as SMP, but I think that's the default today anyways - whether you also compile Dom0 as SMP is up to you. Depending on how much traffic you get through Dom0, it may make sense to do so, but it may also cause more load on the processors from Dom0 which prevents some other domain from running - and that may be more important - depends on what you do in your system, really...  As to allocating processors to domains, the Hypervisor will allocate processors for the domain - but you can tell it what to do. Many people recommend setting a particular processor to be Dom0 always, and not let DomU's run on that processor ever. That reduces the time to switch between DomU and Dom0.

 

5, 6 are answered by Steve.

 

Non-numbered question on "noreboot": Yes, if you shutdown the system with noreboot on the command-line, it will not restart after you shut it down...

--

Mats

---

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of George Styles
Sent: 01 June 2006 12:26
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Moved from Xen 2 to Xen 3... some questions..

Hi,

Ive been using Xen2 for ages, and it great, but ive decided to go to Xen 3.

Ive got it working, but I want to ask a couple of questions about it.

1. There no longer seems to be a seperate DomU and Dom0 built when I build from source. Is this the new policy? this would suit me, as I always used Xen0 kernels in my guest domains anyway.

2. Ive got me a vmx (vanderpool / intel virtualization tech) enabled processor (as shown in cpuflags in /proc/cpuinfo) - can Xen just use it from the default build (make world), or do I have to set any flags at compile time? it didnt winge about missing LibVNCServer, so I assume it wasnt built... ive looked in the manual, but it doesnt seem to say what I need to set to build a vmx version.

3. Still relating to VMX - how can I determine if my bios supports VMX? its a Compaq machine. Does the presence of vmx in /proc/cpuinfo indicate the bios supports it? there are no options in the BIOS about vmx (there is one about NX flag - i realise thats the no execute flag, but that is where I would expect any VMX options to be). Do all bios's that support VMX have an option to enbale / disable it?

If its not enabled, is is possible to 'hack' the bios image to enable it? (i once used a tool to enable IRDA on a bios for a gigabyte motherboard, so I know bios rom images can be tampered with!)

4. The processor in the new box is dual core- do I need to build a SMP version of the Xen hypervisor / Linux kernel to take advantage of this? or does the hypervisor deal with this side of things, and allocate processors to domains?

5. Is there ANY way to see the pre-linux-kernel messages from boot (the messages from the hypervisor)? they scroll past so quickly I cannot read them, then if I get a kernel panic when the Linux kernel starts, I cannot see what the hypervisor was saying. It turned out to be lack of sata drivers in the kernel (they were modules), but that was guesswork. Im sure the Xen boot messages would tell me what hardware it had picked up.

6. When I was trying to build a custom kernel (with the sata drivers in), i tried the usual
make ARCH=xen menuconfig
in the linux source dir, but it gave an error (something about no such target or somesuch).
Is this no longer nescesary? it worked OK when I ommitted the ARCH=xen, but I didnt proceed as I wasnt sure if it would compile in the Xen stuff... whats going on???

(I got it booting in the end by making a ramdisk, so these questions are academic, but I like to understand whats going on)

Finally, if the noreboot option is in the hypervisor parameter lines in grub config, does that prevent software reboot from working in Dom0? ive remotely crashed my Xen box on a reboot, and am hoping thats what it is! (it was its first reboot after booting Dom0 and I still had noreboot in from when I was trying to get Dom0 up)

thanks in advance for any insight :)

George

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