Hi guys, As we know, android audio passthrough latency is not good, many devices have 150ms-250ms total latency. This is unacceptable on realtime applications. And I heard Fastmixer in JB didn't get dramatically improvement on it. So, I tried some ways on ICS to make audio flinger more stable and less latency.
1. I changed the audioflinger mixer thread's scheduler class to SCHED_RR. The old scheduler class is SCHED_OTHER. Although, audioflinger's mixer got the lowset nice value and highest priority, the CFS scheduler can't promise it getting enough resource at any critial time. In my opinion, the realtime scheduler is helpful for a stable audio renderer. Howerver, I'm not sure is this conflicted with the design idea of audioflinger or android arch, any comments? 2. The total audio latency is decided by driver buffer size plus cblk buffer size(IPC buffer for audiotrack and audioflinger). For alsa driver, at least 4 periods were needed for DMA writing, and 10 milliseconds period was accepted by most devices as I tested. Cblk buffer size equals to (driver buffer size)*2, I think it is too large, and changed it to the same value as driver buffer allocated(JB brought Non-block mode, I'm not sure clbk buffer size could be ingored or not in JB Non-block mode). So the total latency would be (10 * 4 + 40) = 80 milliseconds. If your system is reliable in 5 milliseconds level interpret, 40 milliseconds latency reachs. For most devcies, 10 millisecods * 6 is recommended, and total is 120 ms, big buffer is helpful in busy system case. 3. Setting different buffer size for different applications. HD movie playback gets heavy cpu load and latency is neglectable, big buffer size is welcomed. And in MIDI Player, small buffer size brings much better experience.I heard some vendors already configed differnet buffer for special usage. The side effect is restarting your audio device, since many cases don't support buffer size tuning dynamically. Any way, these steps were not good enough, if you tried this before, please reply this thread. Any comments or ideas will be welcomed. Thanks! Charlie -- unsubscribe: android-porting+unsubscr...@googlegroups.com website: http://groups.google.com/group/android-porting
