[jazzplusplus-devel] Thoughts about the linux kernel - observed trends

[D.B. M. <db...@ho...>]

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> Date: Tue, 13 May 2008 22:10:47 -0700


>From thread ;


> Subject: [jazzplusplus-devel] Debian Build and Run Attempt
> 
> RV = Robert Vogel wrote me on Sun, 11 May 2008 23:14:04 -0400
> RV> Hi Pete,

> RV> I tried compiling Jazz++ on my Debian Etch stable system.
> RV> It looked ok throughout the build process, and it produced
> RV> an executable. When I tried opening the executable, it
> RV> didn't prompt for a configuration file, but it found one
> RV> in my home directory. I'm not sure it is the correct
> RV> jazz.cfg though. (attached)



> RV>
> RV> Rosegarden complains every time I start it that the
> RV> 'system timer resolution is too low'. I know I need
> RV> to find a RT kernel, but I've been too cautious to
> RV> try one yet. Soon. That's why I need to be able to
> RV> connect to an external device or to a soft synth.
> RV>


Thanks Robert, you've pointed out something we all know
is a bit of an issue with linux. This really bites too when
considering so called 'realtime' software applications, and
timing sensitive transports like MIDI with linux.

Here's my thoughts and current experience with things
smelling of herring...

Whether Robert really needs to 'find' a  'RT' kernel is
probably up for debate. I mean...I haven't looked lately
but patched&hacked RT kernels are out there, so are 
the patches needed to compile your own, but there is
SO MUCH dated and old documentation out there,
it's not surprising to find comments like this.

There's a lot of the same out there. I actually know
rosegarden (as a piece of software), and I'm also
familiar with that runtime complaint about timer
resolution. Old documentation leads people into 
believing they need an RT kernel - perhaps they do
in certain situations - but most people do not.

What they need to do instead, is reconfigure their
linux source tree, recompile, install, and reboot to
the new kernel. Compiling Jazz++ from svn is a 
doddle for most people compared to a kernel rebuild.

In the configuration phase, they need to set
the kernel timer resolution to 1000Hz. It can also
matter (performance wise) which pre-emption model
 is selected, and what task-scheduling is selected. Or 
even how powerful (or not) their hardware is.... 

It's a minefield -- depending on just which linux distro
people are using, determines exactly which kernel
options were selected and configured in the 'standard'
kernel build. Also, just how easy it might be for people
to fix things themselves largely depends on which
linux distribution they use as much as it does on their
own skills or the instructions they might be following.


I don't want to write yet another kernel howto - I am
prepared to document this issue pretty much like I do 
here, pointing out the issues, giving out clues, but just
because of the large disparity and possible difference
between one linux distro compared to another, the user
is very much  largely on their own with that one.

I'm just wondering if something more can be done about it
...or nothing at all....and I just somehow get the feeling, 
someday this will bite us all....

Regards,

Donald B




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