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The Friday 2007-12-14 at 19:12 -0000, David wrote:
On Fri, 14 Dec 2007 18:28:19 -0000, Jason Craig <[EMAIL PROTECTED]> wrote:
I looked into the topic for a bit, what I was "needing" the RT kernel for
was audio recording/processing. Normal users can't run threads in
"realtime" priority, the super user can, but then running general
applications as the superuser is not really the best idea.
Just an idea... would it be possible to re-nice the program you are using?
There is a problem.
First, it is not renice what you are looking at, but ionice - from the
manual:
This program sets the io scheduling class and pri‐
ority for a program. As of this writing, Linux
supports 3 scheduling classes:
Idle. A program running with idle io priority
will only get disk time when no other program has
asked for disk io for a defined grace period. The
impact of idle io processes on normal system
activity should be zero. This scheduling class
does not take a priority argument.
Best effort. This is the default scheduling class
for any process that hasn't asked for a specific
io priority. Programs inherit the CPU nice setting
for io priorities. This class takes a priority
argument from 0-7, with lower number being higher
priority. Programs running at the same best effort
priority are served in a round-robin fashion.
Real time. The RT scheduling class is given first
access to the disk, regardless of what else is
going on in the system. Thus the RT class needs to
be used with some care, as it can starve other
processes. As with the best effort class, 8 prior‐
ity levels are defined denoting how big a time
slice a given process will receive on each
scheduling window.
Now, you can call a program like this:
ionice -c1 program args
to give it realtime priority. However... ionice has to be run as root. If
you call it being user, through sudo, the effective user of the child
program is still root - and this is not what we want and need.
The alternative method is to use "ionice -c1 -p PROGRAM_PID" instead,
which can be set to be used through sudo, but you need to know the PID of
the process you want to modify the priority. And if it has children, them
too.
But! Some programs try to detect at start if they have realtime
priorities... if they are given them later by the method described, it is
already to late for them, they will not use the alternative algorithms
designed for that case. I believe Xine does this.
So, yes, a method to give a group of programs realtime priority from the
start would be interesting.
- --
Cheers,
Carlos E. R.
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