changes to scheduler from mainline 4.8 to 4.10?

[Bert Schiettecatte]

Hi all,

I'm working on a realtime audio application running on a rk3288
platform. The application is written in the JUCE framework, and uses
ALSA for audio output. I build the application in a debian jessie
chroot since it needs a bunch of libraries compiled for armhf.

The application used to run fine on 4.8 mainline, without noticable
audio dropouts. I had to upgrade recently to 4.10 mainline to get the
audio gadget driver working, but now the application has audio
dropouts (pause in the audio output).

I have been using 44100 hz sample rate and 960 samples buffer size for
testing. I increased the buffer size to 1280 which seemed to improve
things a little, and then after googling around I changed the IO
scheduler to noop (it was set to CFQ), which further increases the
performance. I now only have occasional audio dropouts.

The application does a lot of I/O via HID and has 4 audio processing
threads for signal processing, besides other threads and callbacks for
HID I/O.

Does anyone know if there are specific settings to pay attention to
for running realtime audio processing applications on mainline 4.10,
and if anything has changed with regards to how threads are scheduled,
between 4.8 and 4.10? Just trying to understand why my application
behaves differently now on 4.10 and if this is due to changes that
have been applied and kernel config settings I might not be aware of.

Thanks for helping!
Bert