[LAU] difference between realtime-kernel and low-latency-kernel?

[thomas fisher]

I can supply no quantifications for the 32 bit 2.6.20-16-realtime kernel  in 
ubuntustudio other than no xruns have been observed. With the low latency 
kernel, xruns were observed. Jack is the only app that has a -20 priority 
assigned. The general workstation has been running without fault. The general 
Debian / Ubuntu philosophy tends towards system stability.  
Tom
On Wednesday 03 October 2007 14:54:32 Fernando Lopez-Lezcano wrote:
> On Wed, 2007-10-03 at 18:39 +0200, Frank Barknecht wrote:
> > Hallo,
> >
> > Matthias Schönborn hat gesagt: // Matthias Schönborn wrote:
> > > I've just read that there's a difference between a realtime-kernel and
> > > the low-latency-kernel provided by ubuntustudio. The text in the german
> > > wiki on ubuntuusers.de said, that a realtime-kernel is slightly better
> > > than the lowlatencykernel (http://wiki.ubuntuusers.de/Echtzeitkernel) -
> > > then why isn't it used in ubuntustudio? Or do I just mix something up?
> >
> > I think, this wiki and maybe Ubuntustudio as well are using a very
> > confusing terminology.
> >
> > Generally we have two kinds of kernels: The "vanilla" kernel as
> > downloadable on kernel.org and the same kernel, but patched with Ingo
> > Molnars RT-patches. The vanilla kernel, if configured properly with
> > CONFIG_PREEMPT etc., already gives very good performance in the low
> > latency department, enough for many users, even audio users. I run one
> > of these.
> >
> > If you want more, then you can install a RT-patched kernel, as is
> > provided in the linux-rt or linux-realtime packages.  I would call the
> > Ingo-Molnar-patched kernels Realtime-Kernels or Low-Latency-Kernels.
>
> To further clarify (or confuse?) the issue, how "low latency" the kernel
> is also depends on how you configure the kernel build options before or
> after patching the kernel with Ingo's patch. For Ingo's patch
> CONFIG_PREEMPT_RT is the best option in terms of latency but there are
> others (CONFIG_PREEMPT_DESKTOP) that have a more conservative approach
> but have (relatively speaking) higher latencies. So from worst to best
> it would be something like:
>
>   vanilla linuz + CONFIG_PREEMPT_NONE
>   vanilla + CONFIG_PREEMPT_VOLUNTARY (used by the stock Fedora kernel)
>   vanilla + Ingo + CONFIG_PREEMPT_DESKTOP
>   vanilla + Ingo + CONFIG_PREEMPT_RT (the one I use for Planet CCRMA)
>
> (there's more granularity and options in the CONFIG_PREEMPT* world but
> those are the ones that have the biggest impact as far as I can
> remember)
>
> -- Fernando
>
>
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