Re: [linux-audio-user] ingo molnar patch on mandriva's kernel

On Wed, 15 Feb 2006 20:40:56 +0100
"emanuele ..:: www.rumoridifondo.com ::.." <emanuele@email-addr-hidden> wrote:

> yes, mandriva has it's realtime kernel (the kernel multimedia) but i
> still have xrun when i play soft-synth with a big chord and fast arpeggios.
>
> so i think that mandriva's kernel is not really patched with -rt. but
> maybe it's just an error on configuring my computer or something wrong
> with some hardware.

The -rt patch is not a magic thing to make your computers have doubled
cpu strength. I'd suggest a simple test of which the result would
interest me..

Play one note, then play two at the same time, then three. And so on.
Watch some cpu load program during this (gkrellm, gnome-system-monitor,
top, htop, etc. come to my mind). Pretty much independent of the
softsynth you use, the cpu load should go up when playing more and more
voices.

At some point in time your cpu just isn't fast enough anymore.

I wonder whether this is what you're seeing.

Just to clarify what the -rt patch actually does: Given that your
hardware functions and your priorities in the system are setup
correctly, you should be able to achieve ridicously low latency settings
in jack. Keep in mind though, that this comes at a cost. The CPU
overhead raises significantly depending on what software you use with
shorter latencies (The cpu has to switch tasks much more often with
small buffer sizes).

The other advantage of a -rt kernel is that pretty much regardless of
what latency setting you use you can almost guarantee that no xrun will
ever happen, except for ones induced by faulty jack clients. So even for
people without need for supershort latencies or even moderately short
latencies (i.e. people who only want to record and do no live
input->output processing), the irq priorization setup (and jackd) gives
another level of safeness from xruns. On a vanilla kernel an IRQ can
disrupt jack operation for pretty long times. Properly setup this cannot
happen on a -rt system.

About the setup of irq handlers: The chrt program usually comes in a
package called schedutils. Look out for that or build it from source.

Flo

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