Re: [iiwusynth-devel] Re: [Swami-devel] update and todo list

[Josh Green]

On Mon, 2002-06-03 at 02:31, Tim Goetze wrote:
> Josh Green wrote:
> 
> [...]
> 
> >Yes, performance seems like the most major issue for me. I am currently
> >using a 366mhz PII laptop and I have no trouble in maxing out my CPU. I
> >was also just reminded again today that running Swami/iiwusynth as root
> >is a bad idea. I connected up my little loop sequencer program via the
> >ALSA sequencer and started to crank the tempo up. Computer totally
> >frozen, not even SysRq keys would work, still audible noises emitting
> >though :)  I'm just glad I'm using ext3 journaling. Are there any better
> >ways of getting low latency audio without the perils of SCHED_FIFO?
> 
> no, you can't do without SCHED_FIFO. it's the only way of ensuring
> your process is capable of processing promptly and frequently. without
> it, when the audio interface fires an interrupt and your process
> is marked ready to run in kernel, it is just one among a random
> number of processes contending for cpu. therefore the time it takes
> until your process actually gets to deliver data to (or fetch from) 
> the audio interface is not determinate in SCHED_NORMAL.
> 
> occasionally i manage to lock up this box in SCHED_FIFO and SysRq
> hasn't failed me yet. strange it does this to you. have you checked
> it works at all?
> 
> tim

Yeah, I understand the concepts of SCHED_FIFO, I just wish there was a
better way to achieve high priority status without resorting to being
root and risking the process running away with your entire machine. I
would think someone would have come up with a solution by now, since the
current state of things seems rather dirty. What happens when there is
more than one SCHED_FIFO process?
Perhaps the process 'nice' value could be used for such things. I'm
curious how other Unix OSes handle latency critical applications and
what APIs they provide. Anyways.. Just some thoughts. Lates..
        Josh Green