Re: [Jack-Devel] problem with jack's watchdog killing jackd process after a 3-4 seconds of operation

Athanasios Silis wrote:
> My virtualbox host, is a server (slackware too). so no rt kernel, no
> low-latency desktop and the rest. could that affect the ability of the alsa
> on the host to provide duplex audio functionality?
> In virtualbox I am using the 'alsa' driver and exposing the AC97 codec on
> the guest. HDA intel didn't offer much different results though.

It could, though in my experience the quality of the device emulation
tends to be the limiting factor.  I use KVM's emulated audio devices
for portability testing as part of the work I do on aqualung (playback
software) and I've had the greatest success when I don't
take the guest driver and the emulated device for granted, but rather
experiment with the available combinations to see what works best for
the OS.  With a Linux guest, its less noticable (probably because
Linux gets the most testing) but I've found, for example, a Windows XP
guest in KVM works best with the emulated ES1370, where as OpenBSD
and OpenIndiana runs the smoothest with the AC97 emulation.  I haven't
had much luck getting anything to work well with FreeBSD (though I
haven't tried any guest kernel tuning yet).

> Thank you for your help!
> unfortunately, the plan to have this vm guest as a fx engine can't be
> utilized :(
> 
> BUT (just had a -hopefully- brilliant idea) what if I forget about alsa,
> and I use this jack server as a slave using the net backend????
> could i do that and forget about the real hw ports?

Absolutely.  I do that w/kvm regularly, and I'd recommend it vs. using
emulated hardware in the guest.  Of course it really depends on what
you're actually trying to achieve ... I do this just to route PCM
audio from my sandboxes to my workstation, and I don't do anything
that's terribly performance critical in my sandboxes (one of them is
for a browser instance, the others are mostly for doing portability
testing and trying out software I don't trust).  For example, I've
found I can watch crap on youtube even with X11 forwarding and audio
routed over netjack1 (via loopback mind you... kvm is running on my
workstation, though it should work over a gigE network without any
problems too) with acceptable lag.  I wouldn't try to watch an entire
movie or TV show that way as av sync issues will eventually become
irritatingly distracting, but it's fine for casual surfing.  As for
using a vm for effects processing offload... that's sorta dodgy given
that guests are subject to sharing their processing time, you're
likely going to run into bad latency problems.  That said, it never
hurts to just try it out and see how far you can push things.

-- 
Jamie Heilman                     http://audible.transient.net/~jamie/

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