Re: [Qemu-devel] Audio latency

[malc <av1474@comtv.ru>]

On Thu, 11 Feb 2010, Alberich de megres wrote:

> On Thu, Feb 11, 2010 at 7:53 AM, malc <av1474@comtv.ru> wrote:
> > On Thu, 11 Feb 2010, Alberich de megres wrote:
> >
> >> I'm using the alsa driver.
> >> Even I tried to change some values using the export and some flags
> >> that -audio-help shows, but nothing significant.
> >
> > Please do not top post.
> 
> Sorrry!!
> 
> >
> >>
> >>
> >> On Thu, Feb 11, 2010 at 1:03 AM, malc <av1474@comtv.ru> wrote:
> >> > On Thu, 11 Feb 2010, Alberich de megres wrote:
> >> >
> >> >> Hi!
> >> >>
> >> >> I'm running qemu on suse, and i got a very high audio latency. For
> >> >> example, using windows latency is about 4s and audio gets distorted
> >> >> with little cuts.
> >
> > How do you measure it?
> With a program called dpc latency, it's for windows.
> 
> >
> >> >> On the host side (suse), i changed the audio pci device latency to 99
> >> >> but this only improves a little bit.
> >
> > As in: with setpci?
> Yes. I also tired, on host, to low latency to VGA to 10.

That's completely unrelated latency [1]

> >
> >> >> Other thing i noticed is when lowering video resolution, the audio
> >> >> latency gets better and better.
> >
> > Lowering video resolution of what? Guest, host?
> 
> Yes, it was on guest. Even for example if i change the desktop or
> switch to a text terminal when things works better what suggested me
> that could be something with painting the screen. But i'm not shure if
> its just only a side effect of a bad launch command, or something
> else.
> 
> >
> >> >> I started played with source code, but i'm just a newbie on qemu.
> >> >> Anyone can point some light to me please?
> >> >>
> >> >> thanks guys!!
> >> >
> >> > -audio-help is your friend, from there you can deduce (at the very least)
> >> > which audio driver your qemu uses.
> >> >
> >
> > It would also help to know which version of QEMU you run and exactly how
> > you invoke it.
> 
> You're right..sorry:
> 
> qemu-kvm -cpu core2duo -smp 2 -m 1024 -hda /home/nine/imgs/hda1.img
> -vga std  -usbdevice tablet
>                -name t1  -net nic,macaddr=55:54:00:12:34:56 -net
> tap,ifname=tap1,script=no
>                -soundhw ac97

I can't help you with kvm and windows, that said here are the things
to try:
 a. Vanilla qemu
 b. No smp

And i'm not saying that those will help, just trying to collect more
data points.

P.S. 4 seconds of latency is sortof insane, especially given that
     default buffering for ALSA is nowhere near that, not by a
     longest shot.

[1] http://www.reric.net/linux/pci_latency.html

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