Re: [Qemu-devel] [PATCH] hw/usb/dev-audio.c: make USB audio card sound perfect

[Programmingkid]

On Oct 29, 2015, at 11:08 AM, Stefan Hajnoczi wrote:

> On Wed, Oct 28, 2015 at 09:59:32AM -0400, Programmingkid wrote:
>> 
>> On Oct 28, 2015, at 6:58 AM, Stefan Hajnoczi wrote:
>> 
>>> On Mon, Oct 26, 2015 at 01:24:00PM +0100, Gerd Hoffmann wrote:
>>>>> So this change would make real-time audio feel laggy.
>>>> 
>>>> That is secondary if the sound quality is bad due to constant overruns
>>>> and underruns ...
>>> 
>>> This is like sweeping network performance problems under the rug by
>>> increasing queue size.
>>> 
>>> Before bumping the buffer size and breaking real-time applications (i.e.
>>> 128-512 samples per buffer), there should be a little performance
>>> investigation to understand the root cause.
>>> 
>>> Why are overruns/underruns occurring?
>>> 
>>> Is the problem the host sound API, QEMU's audio/mixing infrastructure,
>>> or guest responsiveness?
>> 
>> I think a better question is who is going to spend the time and energy 
>> trying to answer these questions?
> 
> To push patches like this is arrogant because your patch makes a
> trade-off: smooth playback on *your* system vs worse latency for
> *everyone*.

I'm sorry you are taking this so personally. I would never have submitted this
patch if it causes a lot of problems to others. 

> You don't want to spend time understanding why playback is choppy on
> your system.  That's fine.

I have been working on a sound output related problem for years.


> What bothers me is that you have no qualms about making latency on
> everyone's system worse.

How do you know it makes sound on other people's systems worse? If you have
actually done any testing, I would like to see the results. 

Here is a format I suggest you could use:

Host operating system:
Guest operating system:
emulated machine:
Tests conducted: video playback, game sound playback, ...


> If you don't have time, that's fine.  Just send an email to report the
> symptom and in the meantime use the qdev property to increase the buffer
> size for yourself:
> 
>  -device usb-audio,buffer=6144

The thing is I am certain is this patch makes sound play better. Before this 
patch the sound
played back from the usb audio device was very poor. With this patch it sounds
great. I have played video files in QEMU and if the latency was really high, 
then
I would have noticed the audio not being in sync with the video. 

You have shown calculations, but you haven't given any real world examples
of why this patch is bad.