[alsa-devel] Maximum buffer size on HDA

[Jaroslav Kysela]

On Mon, 16 Jun 2008, Takashi Iwai wrote:

> At Mon, 16 Jun 2008 12:53:11 +0200 (CEST),
> Jaroslav Kysela wrote:
> > 
> > On Mon, 16 Jun 2008, Takashi Iwai wrote:
> > 
> > > At Fri, 13 Jun 2008 21:13:03 +0200,
> > > Lennart Poettering wrote:
> > > > 
> > > > Heya,
> > > > 
> > > > the HDA driver allows a playback buffer size of something like 64K
> > > > onyl. Is this a driver limitation or a limitation of the hardware?
> > > > Skimming through the docs I cannot see anything like this, and I got
> > > > the idea that the audio buffer is maintained in system memory, not
> > > > sound card memory, so why this limit?
> > > 
> > > This comes from the buffer pre-allocator.
> > > Run the below:
> > > 
> > > 	# echo 1024 > /proc/asound/card0/pcm0p/sub0/prealloc
> > > 
> > > then you can use now 1MB buffer.  snd-hda-intel has max
> > > pre-allocation buffer size 1MB, and this is the hard-coded limit.
> > > 
> > > It's rather a silly constraint, and I think it'd be better cut off.
> > > OTOH, this makes the system safer (e.g. avoiding page allocations for
> > > too large buffers), and there is a proper workaround, too.
> > > So, I'm open about this change, so far.
> > 
> > Which workaround you're talking about?
> 
> Reset a proc file manually like the above.  Without this, you cannot
> allocate the buffer over the pre-allocated size.

I'm not quite sure what you like to change. Make 1MB limit smaller? Or 
change the default preallocated size? Or remove preallocation? I think 
that it might make sense to increase the default preallocation value to 
128KB or 192KB.

						Jaroslav

-----
Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.