Re: [LAU] Are RT-patches needed anymore? (Was Re: >= 2.6.27 RT ETA?)

On Fri, 2009-01-30 at 03:23 +0100, torbenh@email-addr-hidden wrote:
> On Thu, Jan 29, 2009 at 03:41:48PM -0800, Fernando Lopez-Lezcano wrote:
> > On Tue, 2009-01-27 at 14:06 +0100, Peder Hedlund wrote:
> > > Quoting Ken Restivo <ken@email-addr-hidden>:
> > >
> > > > And here is the next installment in the saga of trying to get Ingo
> > > > RT going on my Asus EEE.
> > > >
> > > > I successfully built and ran the 2.6.26.8-rt12 with the alsa_seq
> > > > patch. It ran.
> > > >
> > > > The problem is that neither the Ethernet (atl1e) or wireless
> > > > (rt2860sta) work. So I pretty much had to reboot back out of it
> > > > immediately.
> > >
> > > I've been running the standard kernel from openSUSE 11.0 on my Athlon
> > > 2000+ and can get down to at least 5.3ms latency on an Audiophile 2496
> > > using the limits.conf "trick".
> > >
> > > Do people really need lower latencies for music purposes or are we
> > > just thinking "well, I needed the RT patch three years ago; I ain't
> > > stopping now" ?
> >
> > It depends on your usage (this question seems to come up every couple of
> > months lately). The current kernels are much better in low latency
> > applications than three years ago. They are usable if you don't require
> > "low" latencies (64 or 128 x 2). What you get also strongly depends on
> > the hardware mix you have.
> >
> > If you want to use 64 or 128 frame periods (or less) you probably will
> > need at rt patched kernel in most cases. Then again if an occasional
> > xrun is not a problem then you would be fine with the stock kernel.
>
> i am running with -p64 -n3 on an intel-hda with 2.6.28
> of course internal cards have the greatest potential for lowlatencies.
> so this might be unfair, compared to pci.

Hmmm, I'm not sure, the load on pci itself by a soundcard should be
nothing really hard. What would the internal card use? Would not that be
pci or pci express anyway?

> and i havent really seen xruns which i could not relate to some
> programm which wasnt RT-safe, and i am compiling stuff most of the day...
> though perhaps i am not pushing the DSP load hard enough.
>
> i did not even turn preemptible RCU on.
> the latency measurement instrumentation is also in 2.6.28 btw.

Well, that's very good news then!

I think the last time I tried to use a non-preempt was 2.6.27.x (maybe,
I would have to double check). Playing 24 channels in ardour would
result in xruns, not very often but they would happen, this is with
128x2 on an RME hdsp card runing on a quad core intel system. I should
try again with the latest available.

-- Fernando

>
> >
> > While going down to, say, 1 or 2 mSecs of latency might be thought of as
> > unnecessarily low, if your system can work at those levels then you are
> > going to be more likely to never get an xrun when running at 5 mSecs
> > latency. And if you are performing in a concert situation you _don't_
> > want an xrun, not even one. Linux, even rt patched, does not have a hard
> > realtime scheduler with deadline guarantees, etc.
> >
> > -- Fernando
> >
> >
> > _______________________________________________
> > Linux-audio-user mailing list
> > Linux-audio-user@email-addr-hidden
> > http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
>

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Received on Fri Jan 30 08:15:02 2009