Re: [Qemu-discuss] qemu - kvm - Line 6 HD300

[Mike Lovell]

On 07/23/2012 12:46 PM, Johan & Katrien Dewaele² wrote:
> Hi,
>
> I'm confused !
>
> I'm trying to get Line 6 Edit HD 300 software for a Line 6 
> multi-effect-board for guitar to run on a virtual machine on my Debian 
> testing - kernel 3.4.6 box.
>
> 1° I tried virtualbox version 4.1.18-78361~Debian~wheezy with windows 
> XP as guest:
> The program runs, I can adjust all parameters/knobs but have a problem 
> synchronising data (pre-sets) between the software and the Line6 
> hardware: pre-sets are not loaded from the effect-board, adjustments 
> made on the HD 300 edit software can not be saved to the device 
> (hardware).
> So communication between soft and hardware is not optimal.
>
> 2° So I was suggested to try kvm-qemu as this software is being 
> developed more actively
>
> Hence my confusion: Can somebody tell me what the difference is 
> between : qemu and qemu-kvm ?
>
> I have following versions installed:
> qemu 1.1.0+dfsg-1               fast processor emulator
> qemu-kvm 1.1.0+dfsg-3               Full virtualization on x86 hardware
>
> I start the guest OS as follows: (don't mind the difference in shared 
> samba-folder, and the extra parameters for having a network interface 
> in qemu)
>
> $kvm -smb /home/dewaele/bin/shared -m 512 -smp 4  -localtime -device 
> piix4-usb-uhci -usb -usbdevice host:0e41:5057 /mnt/Windisk/QEMU/qemu_XP3
>
> $qemu -netdev user,id=usernet -device rtl8139,netdev=usernet -smb 
> /mnt/MijnDocsDisk -m 512 -smp 4 -localtime -device piix4-usb-uhci -usb 
> -usbdevice host:0e41:5057 -machine accel=kvm,kernel_irqchip=on 
> -option-rom /usr/share/seabios/optionrom/kvmvapic.bin 
> /mnt/Windisk/QEMU/qemu_XP3
>
> For both I use kvm acceleration-virtualisation (I notice an important 
> performance increase when adding the machine accel parameter in qemu), 
> but I do not see any difference in the way the Line 6 program or 
> Windows XP behaves.   I am  using the same windows XP image.
> But hey, both programs seem to be allready better than virtualbox 
> !!!!  synchronisation is somewhat better but still not good enough.
>
> As with both qemu and kvm-qemu the Line6 software is not really 
> behaving as it should, I would like to choose what the best solution 
> is, and will be ....
>
> 3° I tried googling the matter: most people seem also confused.... ;-) 
> : has kvm been merged with qemu or will this happen in the future? Or 
> is kvm a step ahead of qemu?  Is there still  a difference in code?  
> Is qemu only hardware emulation and not real virtualisation as kvm 
> should be (what is the difference)?
>
> 4° also if anybody has more look to have this software communicate 
> better with the Line 6 hardware and would like to share: I would 
> appreciate any help or advice or suggestions.  Hey, I'm open to 
> everything ! :-)
>
> Best regards and thanks in advance,
> Johan

i think your asking two questions here. one is whats the difference 
between qemu and qemu-kvm. another thats how to improve the performance 
of a usb device in the guest.

these days, there aren't many differences between qemu and qemu-kvm. 
qemu started first and was a general purpose machine emulator but 
without any acceleration it was rather slow. it has the ability to 
emulate a wide variety of platforms and hardware including x86, arm, 
powerpc, mips, etc.

i think 'kvm' is an overloaded term and i think of it just as a linux 
kernel module that allows software to use the virtualization extensions 
in modern processors. 'kvm' is also used to refer to the larger 
ecosystem of things related to virtualization using the kvm kernel module.

qemu-kvm is a fork of qemu that added the ability for qemu to use the 
kvm kernel module to accelerate some guests and improve performance. 
there has been a bit of work to merge the changes qemu-kvm did into the 
upstream qemu code-base and a lot of the work has been completed. there 
are still a few things that qemu-kvm has that qemu does not have. qemu 
already has the ability to use the kvm kernel module for acceleration.

unfortunately, i don't have a lot of experience using usb devices with 
qemu/qemu-kvm guests and haven't ever tried the usb passthru. if you 
have newer hardware with the proper support and can spare a few usb 
ports, you could try giving the entire usb controller to the guest. that 
might give you better performance. 
http://www.linux-kvm.org/page/How_to_assign_devices_with_VT-d_in_KVM 
gives some information about it. i followed those basics steps to pass a 
usb3 controller through to a windows guest and tested a usb stick in 
windows.

i hope that all makes sense and answers your questions.

mike