[linux-audio-dev] Linux 2.6 not a latency panacea?

[Roger Larsson]

On Thursday 14 August 2003 00.09, Joshua Haberman wrote:
> I am distressed.  It was my understanding that the 2.5/2.6 kernel branch
> was undergoing significant scheduler and latency work, and that 2.6
> would eliminate the kernel from the list of obstacles of low-latency on
> Linux.  It will have the preemptable kernel patch, the new scheduler,
> and all of Ingo Molnar's low-latency work.  Claims were being thrown
> around that 2.6 would be the lowest-latency operating system on the planet.
>
> So how is it that we're in the 2.6.0-test series and people are
> complaining about audio skipping in **XMMS**, which uses three second
> buffers by default??  If people are getting skips from high-latency
> playback, what hope is there for low-latency audio?  A series of patches
> are coming from both Ingo and Con Kolivas attempting to address this,
> but the fact they are just now throwing around potential solutions
> erodes at my faith that they really understand the problem or how to
> solve it.
>
> Is 2.6.x going to be suitable for low-latency (or even reliable
> high-latency) audio?  Or is it going to be more of the same: patching
> the kernel, tweaking parameters, reading magical incantations, and
> hoping for the best?
>
> Reassure me please!
>
> Josh

This is when running the default scheduler (as non root / non suid root).
Then you are not allowed to use SCHED_FIFO nor SCHED_RR

The problem such a process might run into is if it needs service or
a resource held by a blocked process...

BTW
	There have been discussions about a new scheduling class
	SCHED_SOFTRR. It would be available for all users.
	But the total usage would be limited.

	If SCHED_SOFTRR were overused those processes would run
	out of their timeslice (SCHED_RR never runs out of their timeslice)

	I think this feature would be pretty cool! And adding this for
	latency sensitive bandwith limited streaming applications could
	simplify lots of stuff for the default scheduler...

/RogerL

-- 
Roger Larsson
Skellefteå
Sweden