[Qemu-devel] Re: [PATCH] alsaaudio: increase default buffer sizes

[Jan Kiszka <jan.kiszka@web.de>]

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malc wrote:
> On Tue, 6 May 2008, Jan Kiszka wrote:
> 
>> malc wrote:
>>> On Mon, 5 May 2008, Jan Kiszka wrote:
>>>
>>>> malc wrote:
>>>>> On Sun, 4 May 2008, Jan Kiszka wrote:
>>>>>
>>>>>> Jan Kiszka wrote:
>>>>>>> malc wrote:
>>>>>>>> On Sun, 4 May 2008, Jan Kiszka wrote:
>>>>>>>>
>>>>>
>>>>> [..snip..]
>>>>>
>>>>>>>
>>>>>>> Yeah, great, that was the key! Find below the version that works
>>>>>>> for me
>>>>>>> (on 64 bit 8) ). It even obsoletes my buffer size patch. Please
>>>>>>> merge!
>>>>>>
>>>>>> Declaring the buffer size tweak obsolete was too quick. I still need
>>>>>> more under certain guest load, but now I'm already fine with
>>>>>> DEFAULT_BUFFER_SIZE=4096. Or all in one:
>>>>>
>>>>> I wonder if everyone will be happy with quadrupled latency, apart from
>>>>
>>>> Hmm, I wonder about the scenario where this latency may actually hurt.
>>>> QEMU is not /that/ fast anyway. ;)
>>>
>>> You would be surprised.
>>
>> Tell me more! :->
> 
> The only thing that i care about: DOS demos and to lesser extent old DOS
> games.

And those suffer audibly if you increase QEMU_ALSA_DAC_BUFFER_SIZE?

> 
>>>
>>>>
>>>>> you and this other user on some (kvm was it) mailing list there are no
>>>>> huge outcries of dissatisfaction, then again i'm not sure how many
>>>>> people
>>>>> use ALSA+QEMU or QEMUs+AUDIO in general.
>>>>
>>>> I don't think many users are actually running QEMU (or KVM) against
>>>> ALSA. You have to
>>>> - manually enable it during configure
>>>> - pass QEMU_AUDIO_DRV=alsa (OSS remains default even if ALSA is on - I
>>>>   ran into this trap first.)
>>>
>>> I don't see how it's a trap. You can also enable esd or fmod drivers
>>> in configure along with alsa, which one should be the default?
>>
>> For sure, you need this mechanism with >1 audio backends being enabled
>> in parallel. It's just the question how one is supposed to find out
>> about this additional requirement:
> 
> Being enabled? Did you mean being built in? And what do you mean by
> mechanism, mechanism to do what exactly?

Yes, I meant built-in.

> 
>> $ grep -r QEMU_AUDIO_DRV qemu
>> qemu/audio/audio.c:        "  set QEMU_AUDIO_DRV=wav\n"
>> qemu/audio/audio.c:        "  export QEMU_AUDIO_DRV=wav\n"
>> qemu/audio/audio.c:        drvname = audio_get_conf_str
>> ("QEMU_AUDIO_DRV", NULL, &def);
>>
>> Am I missing some reference? Then sorry in advance.
> 
> What is the question?

Such kind of documentation is not for wimps. You know where to find and
why to use it, but does the average user do?

> [..snip..]
> 
>>
>> Well, probably configurable as well with compat-OSS (real OSS is dead on
>> Linux). The fact is that - not only for me - this sharing does not work
>> out-of-the-box with OSS, while it does with ALSA. Don't ask me why, I'm
>> not an expert on this, I'm rather looking at it from a "normal" user
>> perspective.
> 
> It doesn't with ALSA on this machine, and on the machine next to this
> one, and on machine that lies on the floor. It boils down to how ALSA
> was configured by distribution maintainers.

Chances are generally higher that broken ALSA setups are reported and
fixed than broken OSS emulations.

Jan


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