[Jack-Devel] Fwd: connecting to JACKD2 with low buffer sizes

[Robert Bielik]

Hi Chris,

Not sure how much this helps, but I have been running the audioinjector octocard (6 in/8 out) on a RPi 3, with stable streaming down to 8 frames per buffer, with a distribution called RealtimePi (https://github.com/guysoft/RealtimePi) Unfortunately I don't know the specific kernel details of it.

My exact setup can be found here: http://forum.audioinjector.net/viewtopic.php?f=5&t=2727&start=30#p5749

Problem of course is that the lower the buffer size, the higher the CPU utilization. With 64 frames per buffer, the latency/CPU tradeoff is acceptable (I think with 8 frame per buffer, I had nearly 100% CPU just shoveling audio from input to output, with 64 it's ~10%).

Regards
/Robert

> -----Original Message-----
> From: Jack-Devel <jack-devel-bounces at lists.jackaudio.org> On Behalf Of
> Christopher Obbard
> Sent: den 25 mars 2018 12:32
> To: jack-devel at lists.jackaudio.org
> Subject: [Jack-Devel] Fwd: connecting to JACKD2 with low buffer sizes
> 
> Hi Guys,
> 
> Running jack with a small buffer (-p64 -n2), and connecting with any
> client causes issues.
> With higher buffer sizes, all is OK.
> 
> This is on an ARM embedded system, with a single core 1MHz processor.
> I've set the cpu governor to performance.
> 
> I have a custom compiled 4.14 kernel with omap2plus_defconfig with the
> following config settings:
> > CONFIG_PREEMPT_VOLUNTARY=y
> > HZ_100=y
> > CONFIG_NO_HZ_IDLE=y
> 
> $ jackd -R -P95 -dalsa -dhw:0 -r48000 -p64 -n2
> > JackPosixProcessSync::LockedTimedWait error usec = 5000000 err =
> Connection timed out
> > Driver is not running
> > Cannot create new client
> > CheckSize error size = 32 Size() = 12
> > CheckRead error
> > CheckSize error size = -1 Size() = 4
> > CheckRead error
> > CheckSize error size = 0 Size() = 12
> > CheckRead error
> 
> 
> Also, with higher buffer sizes sometimes I get xruns. After enabling
> alsa debugging, the error is:
> > ALSA: PCM: [Q] Lost interrupts?: (stream=0, delta=221,
> new_hw_ptr=181343, old_hw_ptr=181122)
> 
> Loosing the FIFO interrupts doesn't seem like a great thing.........
> 
> 
> I _think_ the issue is to do with the kernel scheduling, but this why
> I ask the experts :-).
> Can anyone suggest any kernel settings that will improve my situation?
> 
> 
> Many thanks,
> 
> Chris
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