Re: [LAD] 2.6.20 scheduler and buffer underruns

So the story is more interesting now... with SCHED_FIFO I'm seeing
occational delays of about 60 sample frames (@44K) when there is very
little other CPU activity. It still looks like a buffer underrun in
that the audio data is contiguous on both sides of the delay, so I'm
not dropping a buffer. When I load the CPU with another task doing a
while(1) loop, the glitches go away. Hmmm....

On Jul 11, 2007, at 1:57 PM, Darren Gibbs wrote:

> Thanks, cool... that solves the glitching that scales with CPU
> load, I still have more rare glitches (every few seconds) that look
> like buffer underruns. I'm suspect this is because some other
> kernel entity has interrupts turned off when the DMA interrupt
> needs to be serviced to switch buffers. Are there any clever tools
> for figuring out who might be doing this?
>
>
> On Jul 11, 2007, at 12:33 PM, Lee Revell wrote:
>
>> On 7/11/07, Darren Gibbs <tsquank@email-addr-hidden> wrote:
>>> We're doing an ARM-based embedded device, which right now is running
>>> vanilla 2.6.20. For the sake of simplicity we wrote an OSS driver
>>> that's simply double-buffering and writing to the DAC via I2S. We
>>> have a buffer underrun problem that is directly proportional to CPU
>>> load... no glitches when simply cat-ing a file to /dev/dsp, but lots
>>> of glitches when other things are happening on the system. Can
>>> anyone suggest tools/techniques/patches for improving the situation?
>>
>> Run the audio playback app with SCHED_FIFO priority.
>>
>> Lee

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Received on Thu Jul 12 20:15:04 2007