[LAD] Realtime threads and security

[Robin Gareus]

On 02/23/2011 11:22 AM, Olivier Guilyardi wrote:
> Hi,
> 
> On 02/17/2011 10:53 PM, Robin Gareus wrote:
> 
>> /proc/sys/kernel/sched_rt_runtime_us
>> /proc/sys/kernel/sched_rt_period_us
>>
>> <kernel-source>/Documentation/scheduler/sched-rt-group.txt
> 
> There's something which confuses me. But I'm not sure how this realtime period
> settings relate to the audio I/O period.

It only does iff the audio-I/O thread (or process) is executed with
realtime privileges (`man chrt` - man `pthread_setschedparam` ).

if you have a RT_PREEMPT kernel you can also raise the priority of the
audio-device interrupt handler.

Well, it's a bit more complex than that.. not sure if you can go that
way on Android easily.

> On Android, the closest that one can get to hardware in a more or less portable
> way is libaudio [1]. It's Android's audio HAL. This API exposes blocking read()
> and write() calls, with fixed buffer sizes (input and output buffer sizes
> generally do not match, but that's another problem).
> 
> So, this may be a silly/newbie question, but can one access this blocking API
> from a realtime thread? What will happen when it blocks? How does the read/write
> period relate to sched_rt_period_us?
> 
> [1] http://source.android.com/porting/audio.html
> 
> --
>   Olivier