Comment 2 for bug 1648280

EngineSideChain::wakeAll -- 14 microseconds (from one sample)

  0 756 psynch_cvbroad:entry (tid 1488971) ts:1481161657003383000 psynch_cvbroad
              libsystem_kernel.dylib`__psynch_cvbroad+0xa
              QtCore`QWaitCondition::wakeAll()+0x3c
              mixxx`EngineSideChain::writeSamples(float const*, int)+0x109
              mixxx`EngineMaster::process(int)+0xaca
              mixxx`SoundDevicePortAudio::callbackProcessClkRef(unsigned int, float*, float const*, PaStreamCallbackTimeInfo const*, unsigned long)+0x661
              mixxx`(anonymous namespace)::paV19CallbackClkRef(void const*, void*, unsigned long, PaStreamCallbackTimeInfo const*, unsigned long, void*)+0x23
              libportaudio.2.dylib`AdaptingOutputOnlyProcess+0xe7
              libportaudio.2.dylib`PaUtil_EndBufferProcessing+0x1c4
              libportaudio.2.dylib`AudioIOProc+0x392
              CoreAudio`AUConverterBase::RenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int)+0x2c5
              CoreAudio`AUBase::DoRenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, AUOutputElement*, unsigned int, AudioBufferList&)+0x9a
              CoreAudio`AUBase::DoRender(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int, AudioBufferList&)+0x1f8
              CoreAudio`AUHAL::AUIOProc(unsigned int, AudioTimeStamp const*, AudioBufferList const*, AudioTimeStamp const*, AudioBufferList*, AudioTimeStamp const*, void*)+0x6f2
              CoreAudio`HALC_ProxyIOContext::IOWorkLoop()+0x9e7
              CoreAudio`HALC_ProxyIOContext::IOThreadEntry(void*)+0x58
              CoreAudio`HALB_IOThread::Entry(void*)+0x4b
              libsystem_pthread.dylib`_pthread_body+0x83
              libsystem_pthread.dylib`_pthread_body
              libsystem_pthread.dylib`thread_start+0xd

  0 757 psynch_cvbroad:return (tid 1488971) ts:1481161657003397000 psynch_cvbroad
              libsystem_kernel.dylib`__psynch_cvbroad+0xa
              QtCore`QWaitCondition::wakeAll()+0x3c
              mixxx`EngineSideChain::writeSamples(float const*, int)+0x109
              mixxx`EngineMaster::process(int)+0xaca
              mixxx`SoundDevicePortAudio::callbackProcessClkRef(unsigned int, float*, float const*, PaStreamCallbackTimeInfo const*, unsigned long)+0x661
              mixxx`(anonymous namespace)::paV19CallbackClkRef(void const*, void*, unsigned long, PaStreamCallbackTimeInfo const*, unsigned long, void*)+0x23
              libportaudio.2.dylib`AdaptingOutputOnlyProcess+0xe7
              libportaudio.2.dylib`PaUtil_EndBufferProcessing+0x1c4
              libportaudio.2.dylib`AudioIOProc+0x392
              CoreAudio`AUConverterBase::RenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int)+0x2c5
              CoreAudio`AUBase::DoRenderBus(unsigned int&, AudioTimeStamp const&, unsigned int, AUOutputElement*, unsigned int, AudioBufferList&)+0x9a
              CoreAudio`AUBase::DoRender(unsigned int&, AudioTimeStamp const&, unsigned int, unsigned int, AudioBufferList&)+0x1f8
              CoreAudio`AUHAL::AUIOProc(unsigned int, AudioTimeStamp const*, AudioBufferList const*, AudioTimeStamp const*, AudioBufferList*, AudioTimeStamp const*, void*)+0x6f2
              CoreAudio`HALC_ProxyIOContext::IOWorkLoop()+0x9e7
              CoreAudio`HALC_ProxyIOContext::IOThreadEntry(void*)+0x58
              CoreAudio`HALB_IOThread::Entry(void*)+0x4b
              libsystem_pthread.dylib`_pthread_body+0x83
              libsystem_pthread.dylib`_pthread_body
              libsystem_pthread.dylib`thread_start+0xd