Re: Sound userspace drivers (fishing for insight)

[John Richard Moser <nigelenki@comcast.net>]

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Jaroslav Kysela wrote:
> On Tue, 7 Mar 2006, John Richard Moser wrote:
> 
>> In general, transporting sound data in and out of kernel space is a
>> horrid thought.  Consider the latencies, which all real-time audio
>> people will quickly get angry about.  Write sound; context switch; sound
>> in driver; context switch back.  This over and over?  Now we all know
>> better than that.
> 
> Nope. If you have a cache coherent architecture like x86, ALSA mmaps 
> directly the DMA buffer to application and even pointers to this buffer 
> are mmaped, thus there is no content switch when apps are doing r/w and 
> there is "zero data copy". The only contents switch is when apps call
> poll(), but you should do it, otherwise you'll eat all cpu time.
> 

Awesome.  Nice design  :)  I hath learned today and I woke up 10 minutes
ago.

>> into the kernel; with alsa it's written to a /proc interface, which
> 
> Using /proc? Where? I've not noticed it :-)

I thought that was what /proc/asound/card0/ was for?  :)
> 
> 						Jaroslav
> 
> -----
> Jaroslav Kysela <perex@suse.cz>
> Linux Kernel Sound Maintainer
> ALSA Project, SUSE Labs
> 

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