Florian Paul Schmidt mista.tapas at gmx.net
Tue Aug 15 08:02:25 UTC 2006

On Sun, 13 Aug 2006 15:07:04 +0200
Dominique Michel <dominique.michel at citycable.ch> wrote:

> From http://www.jacklab.net/phpBB2/viewtopic.php?t=103 :
> "Model 1: " Want to start a synth from time to time"
> SUSE Standard kernel with PAM from Rui (also available in the jacklab
> repository)
> Model 2 "Want to work with MusE or Rosegarden from time to time"
> JAD kernel and PAM (Because the SUSE Standard Kernel have no midi RT
> tick for sequencers)
> Model 3 " I want make some fat production / live performing with many
> native FX and soundgenerators with less then 10ms audiolatency" JAD
> Kernel and RT-LSM (WARNING: RT-LSM can maybe crash your system)"
> It is other websites that say exactly the same.

Many websites saying the same thing doesn't nessecarily make this true.
Of course there are some subtle differences between rlimits and the
realtime lsm:

- rlimits allow specifying a maximum priority which uers processes are
allowed to aquire

- rt lsm otoh gives the user the ability to use any rt priority [or none
at all]

- rlimits allow specifying a maximum memory size for mlocking.

- rt lsm otoh again gives the user the ability to use any amount [or
none at all]

- rlimits allow specifying a maximum niceness which user processes are
allowes to aquire

- rt lsm otoh ... [well you get the picture]

The point being that rlimits allow for finer control of what a user
process is allowed to do. So depending on how you have rlimits
configured, you might get differing results from a rt lsm installation.
So let me rephrase my statement:

Given that you have setup rlimtis and rt lsm in equivalent ways, there
must be no measurable difference in achievable latencies. If you do
measure differences, some other factor of your setup differs, too.

Like i said: To my knowledge rt lsm and rlimits are just two different
ways to achieve the same thing: Giving user processes rt scheduling,
mlocking and negative niceness.

As my experience with rlimtis is limited, i still have one more question
regarding the funcitonality of rlimits. It once was discussed on the
mailing lists to include cpu usage throtteling for user processes (i.e.
max. 90% cpu usage, so that runaway processes cannot fully lock the
box). Has this been implemented?

> Another issue is at I was a few times in trouble with the PAM-rlimits
> feature that kill any application that is doing a very high processor
> use. So, I definitely prefer the realtime-lsm.

I don't know that rlimits kill processes on high cpu load. Never heard
of this feature.


Palimm Palimm!

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