[alsa-devel] [LAD] How to get correct midi timings from ALSA using the library only

Florian Schmidt mista.tapas at gmx.net
Wed Jul 25 11:25:29 CEST 2007

On Wednesday 25 July 2007, Carlo Florendo wrote:

> > Try running your process with SCHED_FIFO scheduling and a high prio of
> > e.g. 99.
> I've tried that in kernel 2.4 and I get the same latency results.  Let me
> try tweaking that though by running the system with high priority.  The
> reason why I'd like to make it work in 2.4 kernels is so that existing
> systems with 2.4 kernels could run the app without need for a kernel patch.

2.4.x kernels are terribly unsuited to do any serious sort of realtime work, 
be it audio or midi. 

From my experience this is a classification with increasing suitedness for 
realtime work:

1] vanilla 2.4.x
2] patched 2.4.x [lowlatency patches]
3] vanilla 2.6.x
4] patched 2.6.x [ingo molnar's realtime preemption patches]

There really should be like 100 bogus places between 2] and 3] and another 100 
between unpatched and patched 2.6.x because 2.6.x really is vastly better 
than 2.4.x and -rt patched 2.6.x actually is a realtime system which can be 
made to work up to microsecond resolution [not millisecond ;)].

> Your ideas have been most helpful :)

No problem. BTW: even when you use ALSA queues, the kernel still plays a big 
role. Then it's simply ALSA's responsibility to provide good timing and it 
basically uses the same mechanisms as a userspace program would.

So thrash 2.4.x for all realtime purposes.. 


Palimm Palimm!

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