On Fri, Nov 5, 2010 at 1:58 PM, Clemens Ladisch <clemens@xxxxxxxxxx> wrote: > Adam Rosenberg wrote: >> On Fri, Nov 5, 2010 at 10:31 AM, Clemens Ladisch <clemens@xxxxxxxxxx> wrote: >> > How much CPU does "aplay -D hw -t raw -f dat /dev/zero" use? >> >> I do not know how to calculate CPU usage for a given process. > > The time utility (if you have it) measures both elapsed and actually > used CPU time. I am not sure how to interpret this, but I told aplay to play for 3 minutes from /dev/zero and here are the results: root:/> time aplay -d 180 -D hw -t raw -f dat /dev/zero Playing raw data '/dev/zero' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo real 3m 0.10s user 0m 0.22s sys 0m 8.48s > >> For the audio playback I am polling the streams using >> snd_pcm_avail_update() and then writing the number of frames available >> using snd_pcm_writei(). > > And what does your program do when avail_update returns 0 frames? If it returns 0 then I do not write any frames. I then check the next stream. This continues in an infinite loop. > You cannot write data faster than it's playing; the audio ring buffer > has a finite size. > > You would have a problem if the processing and/or the driver would > make everything so slow that you wouldn't be able to write new data > to the device fast enough, which would result in an buffer underrun. > Does this actually happen? I am currently writing the decoded mp3 data to a buffer in RAM so that the program is decoding the mp3 data as fast as it can. I then run the audio process separately and just play silence. I am doing this so that I can tell how much time is being spent decoding mp3 data and processing audio data so that I know how much time remains for other tasks. From the times I have calculated I can tell that a buffer underrun would occur frequently if I was actually writing the decoded mp3 data to the pcm streams. -Adam _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
