The different realtime kernels
ronan at jouchet.fr
Thu Sep 30 17:58:40 BST 2010
On Thu, Sep 30, 2010 at 11:45 AM, Ralf Mardorf
<ralf.mardorf at alice-dsl.net> wrote:
> Why does Ubuntu Studio comes without PREEMPT RT, but just PREEMPT?!
> This is my intension.
> FWIW, I'm a professional audio and video engineer and did program oldish
> computers and I'm missing hard real-time for modern PCs. Even the
> kernel-rt isn't able to do hard real-time, so I don't understand why
> Ubuntu Studio does prefer a kernel without rt-patch. Today the rt-patch
> isn't good enough and any kernel without this patch is useless for
> multimedia production.
> So a misunderstanding ;)!
You keep coming back to -rt/-realtime, but nobody ever questioned
their greatness. I trust you when you mention -rt is the ideal
solution in your heavy MIDI use case, and I would also *love* a
properly maintained -rt kernel in Studio.
Now, whether we want it or not, the facts are:
- Preparing -realtime (vanilla+rtpatch) or -rt
(vanilla+ubuntusauce+rtpatch) is a lot of work and there are no
resources for this
- On the contrary, -lowlatency (generic with some config tweaks) means
performance tradeoff, _but_ could happen in a PPA (maybe even in the
archives in Natty) because it is less of a maintenance hell
You mention you have some custom built kernels, so if you feel like
helping maintaining -realtime/-rt, by all means step in, talk to
Alessio and make it happen. But insisting again and again on -rt and
-realtime without considering the possibilities is only going to
discourage him from working on the feasible options.
He tries to propose sustainable options and the only echoes are
negative, without much questioning. What are the results of your own
tests with -lowlatency? What kind of performance drop have you met on
one of your heavy setups? How much latency lost, on which kind of
machine / firewire card?
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