14 Oct
2007
14 Oct
'07
12:48 a.m.
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(a)commspeed.net> 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:
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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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