[Bug 772872] audioconvert: superfluous quantization when converting S24LE to S24LE causing extra CPU load

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=772872

--- Comment #17 from Petr Kulhavy <brain at jikos.cz> ---
With exactly the same caps on both sides
audio-converter.c:converter_passthrough() is not called at all, as oppose to
what I originally thought. So this is OK.

But there is still a 2% CPU difference between:

gst-launch-1.0 audiotestsrc is-live=true samplesperbuffer=48 !
"audio/x-raw,format=(string)S32LE,rate=(int)48000,channels=(int)2,channel-mask=(int)0x3"
! audioconvert !
"audio/x-raw,format=(string)S32LE,rate=(int)48000,channels=(int)2,channel-mask=(int)
0x3" ! fakesink

and 

gst-launch-1.0 audiotestsrc is-live=true samplesperbuffer=48 !
"audio/x-raw,format=(string)S32LE,rate=(int)48000,channels=(int)2,channel-mask=(int)0x3"
! fakesink

which I don't see a particular reason for.

After some deeper profiling I'm starting to believe that this is due to heavy
cache misses and lot of processing in gst_audio_convert_submit_input_buffer():

   DLmr       Ir
-- line 790 ----------------------------------------
     .         .      return TRUE;
     .         .  
     .         .    return FALSE;
     .         .  }
     .         .  
     .         .  static GstFlowReturn
     .         .  gst_audio_convert_submit_input_buffer (GstBaseTransform *
base,
     .         .      gboolean is_discont, GstBuffer * input)
     .   207,660  {
     .         .    GstAudioConvert *this = GST_AUDIO_CONVERT (base);
     .         .  
     2   155,745    if (base->segment.format == GST_FORMAT_TIME) {
51,713   363,405      input =
182,156 29,903,118  => ???:gst_audio_buffer_clip (51915x)
     .         .          gst_audio_buffer_clip (input, &base->segment,
this->in_info.rate,
     .         .          this->in_info.bpf);
     .         .  
     .   103,830      if (!input)
     .         .        return GST_FLOW_OK;
     .         .    }
     .         .  
77,937   467,235    return GST_BASE_TRANSFORM_CLASS
(parent_class)->submit_input_buffer (base,
     8 14,328,618  => ???:0x0003f070'2 (51915x)
     .         .        is_discont, input);
     .         .  }



and in gst_capsfilter_prepare_buf():

   DLmr       Ir
-- line 391 ----------------------------------------
     .         .   * This ensures that caps event is sent if we can, so that
pipelines like:
     .         .   *   gst-launch filesrc location=rawsamples.raw !
     .         .   *       audio/x-raw,format=S16LE,rate=48000,channels=2 !
alsasink
     .         .   * will work.
     .         .   */
     .         .  static GstFlowReturn
     .         .  gst_capsfilter_prepare_buf (GstBaseTransform * trans,
GstBuffer * input,
     .         .      GstBuffer ** buf)
21,037   519,150  {
     .         .    GstFlowReturn ret = GST_FLOW_OK;
     .         .    GstCapsFilter *filter = GST_CAPS_FILTER (trans);
     .         .  
     .         .    /* always return the input as output buffer */
     .   103,830    *buf = input;
     .         .  
    18   415,320    if (GST_PAD_MODE (trans->srcpad) == GST_PAD_MODE_PUSH
     4 1,661,280        && !gst_pad_has_current_caps (trans->sinkpad)) {
357,815 29,280,131  => ???:0x048c2088 (103830x)

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