Re: [LAU] KVM virtual machines and jack

On Sat, Dec 12, 2009 at 12:50 AM, torbenh <torbenh@gmx.de> wrote:
> On Fri, Dec 11, 2009 at 08:09:36PM -0600, Reuben Martin wrote:
>> On Fri, Dec 11, 2009 at 9:18 AM, torbenh <torbenh@gmx.de> wrote:
>> > On Mon, Dec 07, 2009 at 01:48:04AM -0600, Reuben Martin wrote:
>> >> On Sun, Dec 6, 2009 at 4:14 AM, Patrick Shirkey
>> >> <pshirkey@boosthardware.com> wrote:
>> >> >
>> >> > On 12/06/2009 03:20 PM, Reuben Martin wrote:
>> >> >> On Sat, Dec 5, 2009 at 8:39 PM, Paul Davis<paul@linuxaudiosystems.com>  wrote:
>> >> >>
>> >> >>> On Sat, Dec 5, 2009 at 2:51 PM, Reuben Martin<reuben.m@gmail.com>  wrote:
>> >> >>>
>> >> >>>> Does anybody know if it is possible to run a guest OS under KVM and
>> >> >>>> have the ins and outs of the virtual audio device presented to that
>> >> >>>> OS, interface with JACK on the host linux system?
>> >> >>>>
>> >> >>>> I've done a little googling on this but couldn't find anything.
>> >> >>>> (mostly because "jack" is ambiguous, and "KVM" can mean a lot of
>> >> >>>> things)
>> >> >>>>
>> >> >>> unless the VM software that provides fake audio devices to the guest
>> >> >>> OS knows about JACK internally or can be configured to use it, this is
>> >> >>> not happening.
>> >> >>> on the other hand, if the VM software can simply use the ALSA JACK
>> >> >>> plugin, that could potentially work (lots and lots of latency though).
>> >> >>>
>> >> >>>
>> >> >> In that case I guess my best bet would probably be to petition KVM
>> >> >> development to add support for JACK. Currently I believe it supports
>> >> >> ALSA, OSS, SDL and PulseAudio.
>> >> >>
>> >> >>
>> >> >
>> >> > If KVM already supports those api's then it can  be used with jack via
>> >> > several different methods. What is the problem that you are having exactly?
>> >> >
>> >>
>> >> No problems yet. I'm putting together a new system and had thought of
>> >> using Windows and Mac as guest VM systems under KVM for running things
>> >> that don't exist for Linux and/or don't work well with WINE. And I
>> >> wanted to see if anybody had tried routing the VM audio ins / outs to
>> >> JACK rather than directly to an audio sink.
>> >>
>> >> Wanted to see if anybody had seriously tried this before I gave it a go.
>> >
>> > using netjack and the master running at -p1024 seems to be working fine.
>> > at least when i compress the audio, and there is not too much gfx memory
>> > transfers.
>> >
>> > i have put a windows build of jacknone-0.4 on http://netjack.sf.net
>> > this is basically jack-1.9.4 with qjackctl and a fixed audioadapter.
>> > it includes netone with celt-0.7 and jack_trans2midi which generates
>> > midi clock... so you can sync your windows apps to jack transport.
>> >
>> >
>> > --
>> > torben Hohn
>> >
>>
>> Very nice. The part about having an ASIO based netjack interface is a
>> key element that I was not aware existed.  And the jack-midi virtual
>> device solves the transport issue as well. I need to give this a try
>> once I finish building my new system.
>>
>> I'll also be interested to see how well routing netjack connections
>> between a windows guest and mac guest works out. Should be
>> interesting.
>>
>> Perhaps in cases like this where more than one jack process is
>> competing for processor time, Round Robin scheduling might work
>> better...
>
> only if you were using zero-latency mode.
> but i dont think you can use that with a VM.
>
> netjack lowers the scheduling requirements
> of the slave a bit.
>
>>
>> I'm interested to see how KVM compares to VirtualBox. From what I
>> understand it's a bit faster / lower latency because it "runs closer
>> to the metal" compared to VirtualBox / Xen / VMware.
>
> yup. me too. can it run win7 yet ?
> i dont have a real choice, because win7 is the only OS, MS gave out for
> free.
>
> the basic problem with VMs is that they seem to have a single thread
> emulating the hardware, so if a big gfx operation is in progress, the
> network processing will get deferred.
> (at least in VirtualBox)
>
> maybe this doesnt happen with the VM audio.

I guess that depends how well the VM host software is multithreaded
and how many cores are allotted to the guest. (assuming you're using
an SMP system)

KVM should handle win7 just fine. Win7-RTM is listed as supported since KVM-88.

-Reuben
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Received on Tue Dec 15 04:15:01 2009