Switch to dmix pure by default?

Switch to dmix pure by default?

[Martin Pitt]

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Hi ALSA developers!

I'm Martin Pitt, one of Ubuntu's core developers, and I hacked a fair
bit around a better audio support in our latest release. We currently
use ALSA 1.0.9 (thus with dmix enabled by default) and use esd on top
of that since dmix pure still does not work on too many cards
(including the powermac driver on my iBook).

However, since esound sucks particularly in terms of A/V
synchronisation and has annoying bugs, and the whole concept of a
desktop sound daemon is more like a workaround than a sane piece in
the software stack, we would like to drop esound entirely and just use
ALSA by default in the future. I imagine that this is true for other
Linux distros as well.

Now I have several questions:

 1) Are you guys interested in reports about cards which do not work
 with dmix (at least not with the default configuration)?

 2) Is there a document which describes dmix debugging, so that we can
 already pre-process bug reports, can sort them out faster, make it
 easier for you, and maybe even can help you with fixing?

 3) As it appears to me, dmix is a pure software mixing plugin, thus
 from the mere concept, it seems hardware agnostic to me. Why does it
 fail on some hardware in the first place?

Thank you in advance, and have a nice day!

Martin

-- 
Martin Pitt        http://www.piware.de
Ubuntu Developer   http://www.ubuntu.com
Debian Developer   http://www.debian.org

In a world without walls and fences, who needs Windows and Gates?

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Re: Switch to dmix pure by default?

[Thierry Vignaud]

Martin Pitt <martin.pitt@ubuntu.com> writes:

>  1) Are you guys interested in reports about cards which do not work
>  with dmix (at least not with the default configuration)?

at least snd-ice1724 lacks dmix and needs it



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Re: Switch to dmix pure by default?

[Takashi Iwai]

At Wed, 19 Oct 2005 17:44:20 +0200,
Martin Pitt wrote:
> 
> Hi ALSA developers!
> 
> I'm Martin Pitt, one of Ubuntu's core developers, and I hacked a fair
> bit around a better audio support in our latest release. We currently
> use ALSA 1.0.9 (thus with dmix enabled by default) and use esd on top
> of that since dmix pure still does not work on too many cards
> (including the powermac driver on my iBook).

Oh, it already works on 1.0.10rc2.

> However, since esound sucks particularly in terms of A/V
> synchronisation and has annoying bugs, and the whole concept of a
> desktop sound daemon is more like a workaround than a sane piece in
> the software stack, we would like to drop esound entirely and just use
> ALSA by default in the future. I imagine that this is true for other
> Linux distros as well.
> 
> Now I have several questions:
> 
>  1) Are you guys interested in reports about cards which do not work
>  with dmix (at least not with the default configuration)?

Most of these cards are not dmixized just because not confirmed to
work - or known as non-workable.  So, it would be helpful to point out
that which cards work with dmix indeed.

>  2) Is there a document which describes dmix debugging, so that we can
>  already pre-process bug reports, can sort them out faster, make it
>  easier for you, and maybe even can help you with fixing?

Heh, documentation is always a problem ;)
There is no general method for debugging dmix, AFAIK.

If you cannot play something, it's either a permission problem, a race
among processes, or a remaining bug.  In this case, running with
strace would help a lot.

If it's the problem of output quality, use "hw" instead of "dmix" with
the same configuration (rate, period/buffer size, etc), and compare.

If it's a latency problem, check the dmix period_size or period_time
configuration.

Last but not least, try the latest version of ALSA.
Many bugs have been fixed since 1.0.9 release.


>  3) As it appears to me, dmix is a pure software mixing plugin, thus
>  from the mere concept, it seems hardware agnostic to me. Why does it
>  fail on some hardware in the first place?

dmix uses mmap, and assumes fine enough periods.  So, it wouldn't work
well the cards supporting only 2 periods, for example.

This kind of limitation can be reduced by introducing a new timer
interrupt syncing with PCM, but it's still under development (in other
words, deep in my TODO list :)


Takashi


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Re: Switch to dmix pure by default?

[Mike Hearn]

On Wed, 19 Oct 2005 19:02:23 +0200, Takashi Iwai wrote:
> dmix uses mmap, and assumes fine enough periods.  So, it wouldn't work
> well the cards supporting only 2 periods, for example.

Is that for performance? I don't really understand why dmix can't just,
well, mix the streams together and then forward it on as a regular
bytestream using the non-mmap interface. Esound works with any hardware,
so couldn't dmix have a compatibility mode?

thanks -mike



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Re: Re: Switch to dmix pure by default?

[Takashi Iwai]

At Wed, 19 Oct 2005 19:17:37 +0100,
Mike Hearn wrote:
> 
> On Wed, 19 Oct 2005 19:02:23 +0200, Takashi Iwai wrote:
> > dmix uses mmap, and assumes fine enough periods.  So, it wouldn't work
> > well the cards supporting only 2 periods, for example.
> 
> Is that for performance? I don't really understand why dmix can't just,
> well, mix the streams together and then forward it on as a regular
> bytestream using the non-mmap interface. Esound works with any hardware,
> so couldn't dmix have a compatibility mode?

The question is not doable or not.  It's a completely different
design.

The mix "server" like esound does:
- _read_ the data from clients
- mix them
- wright them to h/w
Because of this mechanism, it requires smaller period to achieve the
low latency.

OTOH, dmix lets its processes mixing by themselves.  There is no read
or write server operation, i.e. there is no real mix "server".
(In practice, dmix has a resource server, which is used only to pass
 the file descriptor for mmap.)
Each client mmaps the very same h/w buffer, and add/sub the data on
the buffer atomically as write.

Of course, it's possible to implement ALSA-mixing server a la
esound/arts for the hardwares without mmappable buffers.
But, it's just an idea and a plan, so far.  Volunteers are always
appreciated ;)


Takashi


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Re: Re: Switch to dmix pure by default?

[Patrick Shirkey]

HI,

This has possibly become the most regularly requested feature. Is there a
tasklist that has this as a priority?

Cheers.

Quoting Takashi Iwai <tiwai@suse.de>:

> At Wed, 19 Oct 2005 19:17:37 +0100,
> Mike Hearn wrote:
>>
>> On Wed, 19 Oct 2005 19:02:23 +0200, Takashi Iwai wrote:
>> > dmix uses mmap, and assumes fine enough periods.  So, it wouldn't work
>> > well the cards supporting only 2 periods, for example.
>>
>> Is that for performance? I don't really understand why dmix can't just,
>> well, mix the streams together and then forward it on as a regular
>> bytestream using the non-mmap interface. Esound works with any hardware,
>> so couldn't dmix have a compatibility mode?
>
> The question is not doable or not.  It's a completely different
> design.
>
> The mix "server" like esound does:
> - _read_ the data from clients
> - mix them
> - wright them to h/w
> Because of this mechanism, it requires smaller period to achieve the
> low latency.
>
> OTOH, dmix lets its processes mixing by themselves.  There is no read
> or write server operation, i.e. there is no real mix "server".
> (In practice, dmix has a resource server, which is used only to pass
> the file descriptor for mmap.)
> Each client mmaps the very same h/w buffer, and add/sub the data on
> the buffer atomically as write.
>
> Of course, it's possible to implement ALSA-mixing server a la
> esound/arts for the hardwares without mmappable buffers.
> But, it's just an idea and a plan, so far.  Volunteers are always
> appreciated ;)
>
>
> Takashi
>
>
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>



--
Patrick Shirkey - Boost Hardware Ltd.
Http://www.boosthardware.com
Http://www.djcj.org/ - The Linux Audio Users guide
Http://www.djcj.org/gigs - Gigs Guide Korea
========================================

Being on stage with the band in front of crowds shouting, "Get off! No!
We want normal music!", I think that was more like acting than anything
I've ever done.

Goldie, 8 Nov, 2002
The Scotsman



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Re: Re: Switch to dmix pure by default?

[Lee Revell]

On Sun, 2005-10-23 at 15:04 +0200, Patrick Shirkey wrote:
> HI,
> 
> This has possibly become the most regularly requested feature. Is there a
> tasklist that has this as a priority?

You mean dmix by default?  It already works that way.

Lee



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