kc3-lang/SDL/src/audio/alsa

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• Hash : c5914295
  Author :
  Date : 2018-05-04T21:21:32
  

  alsa: avoid hardware parameters with an excessive number of periods.
  
  The previous code attempted to use set_buffer_size / set_period_size
  discretely, favoring the parameters which generated a buffer size that was
  exactly 2x the requested buffer size. This solution ultimately prioritizes
  only the buffer size, which comes at a large performance cost on some machines
  where this results in an excessive number of periods. In my case, for a 4096
  sample buffer, this configured the device to use 37 periods with a period size
  of 221 samples and a buffer size of 8192 samples. With 37 periods, the SDL
  Audio thread was consuming 25% of the CPU.
  
  This code has been refactored to use set_period_size and set_buffer_size
  together. set_period_size is called first to attempt to set the period to
  exactly match the requested buffer size, and set_buffer_size is called second
  to further refine the parameters to attempt to use only 2 periods. The
  fundamental change here is that the period size / count won't go to extreme
  values if the buffer size can't be exactly matched, the buffer size should
  instead just increase to the next closest multiple of the target period size
  that is supported. After changing this, for a 4096 sample buffer, the device
  is configured to use 3 periods with a period size of 4096 samples and a buffer
  size of 12288 samples. With only 3 periods, the SDL Audio thread doesn't even
  show up when profiling.
  
  Fixes Bugzilla #4156.
  

• Files

• SDL_alsa_audio.c
• SDL_alsa_audio.h

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