Re: A bunch of questions about getting a working NetBSD/xen system

[Steven Bellovin <smb%cs.columbia.edu@localhost>]

On Feb 2, 2010, at 7:03 PM, Greg Troxel wrote:

> 
>>   It does not appear that my BIOS supports this though. If I use
>>   "cpuctl identify" I do not see the "VT" instruction listed, and
>>   nowhere in my dmesg output do I have an indication that it's
>>   turned off in the Bios as some sources (NetBSD wiki's xen page)
>>   suggest.
> 
> Look at 'xen dmesg'.  I have a box running xen 3.1.4 with an amd64
> XEN3_DOM0 kernel, and it has both amd64 XEN3_DOMU and i386 XEN3PAE_DOMU
> (or whatever it's called) guests.  My dmesg shows:

I assume you mean 'xm dmesg' -- I don't have a 'xen' command.
> 
> (XEN) System RAM: 2020MB (2069292kB)
> (XEN) Xen heap: 14MB (15156kB)
> (XEN) Domain heap initialised: DMA width 32 bits
> (XEN) Processor #0 6:15 APIC version 20
> (XEN) Processor #1 6:15 APIC version 20
> (XEN) IOAPIC[0]: apic_id 2, version 32, address 0xfec00000, GSI 0-23
> (XEN) Enabling APIC mode:  Flat.  Using 1 I/O APICs
> (XEN) Using scheduler: SMP Credit Scheduler (credit)
> (XEN) Detected 2999.745 MHz processor.
> (XEN) VMX disabled by Feature Control MSR.
> (XEN) CPU0: Intel(R) Core(TM)2 Duo CPU     E6850  @ 3.00GHz stepping 0b
> (XEN) Booting processor 1/1 eip 90000
> (XEN) VMX disabled by Feature Control MSR.
> (XEN) CPU1: Intel(R) Core(TM)2 Duo CPU     E6850  @ 3.00GHz stepping 0b
> (XEN) Total of 2 processors activated.
> 
> and I think this is a VMX-capable machine.

Note that it explicitly says that it's disabled by the "Feature Control MSR" -- 
on my box, I know that there's a BIOS option for it.
> 
>>   Can I use netbsd-5 instead of -current for DOM0/PAE yet?
> 
> in production here, no issues - with PV mode.
> 
>> 3. I have DOM0 working with -current. But it seems awfully slow! Disk
>>   I/O and also net I/O seem to be much slower than normal. Is there
>>   anything that needs to be done to have reasonable performance in
>>   DOM0. Will the DOMU's be able to perform well despite the slowness
>>   in DOM0?
> 
> That sounds messed up.  I have not observed dom0 to be noticeably slower
> than running on bare metal w/o xen.
> 
> For domU disks, I make files in the dom0 filesystem, and vnconfig them.
> I found that dd from a file is ~90% of the speed of the disk, and dd
> From the 'raw disk' in the domU is again 90% of that, or something more
> or less like that.  Basically there was a noticeable hit but not a big
> deal.


I do the same thing.  I don't have spare disks, and dedicating fdisk partitions 
is too inflexible.  In the past, I've had to allocate larger vnds to some of my 
VMs as usage grew; that wouldn't be easy if I'd used fdisk pa

                --Steve Bellovin, http://www.cs.columbia.edu/~smb