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

i have actually had no end of trouble with ubuntustudio's (and now ubuntu's)
rt kernel. on an amd 6000+ system with 1gig ram and a rme9652 soundcard i
can't get reliable performance under 40 or so ms. i even tried a vanilla
kernel with the rt patches and had the same trouble. the 64studio kernel
worked fine, however. i'm currently running at 5ms with it and have had no
problems. this is even with compiz fusion running and spinning the cube
whilst playing back audio from an 18 channel ardour project. what patches
would cause such a difference in performance? it isn't any options selected
in 'make menuconfig' - i loaded the 64studio's ones in and used them. still
no luck. i can only assume they have added more patches to do with realtime
performance than just the -rt patchset. any ideas?

porl

On 05/10/2007, thomas fisher <studio1@email-addr-hidden> wrote:
>
> I can supply no quantifications for the 32 bit 2.6.20-16-realtimekernel 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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> > Linux-audio-user@email-addr-hidden
> > http://lists.linuxaudio.org/mailman/listinfo.cgi/linux-audio-user
>
>
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Received on Sun Oct 14 08:15:01 2007