[Beowulf] preemptive kernel and preemptive schedulers

Lombard, David N dnlombar at ichips.intel.com
Mon Jun 25 08:06:04 PDT 2007

On Fri, Jun 22, 2007 at 10:05:12AM +0530, Balamurugan.R wrote:
[something in HTML, that I didn't want to muck about with in Mutt]

As Mark Hahn mentioned, the two schedulers you're looking at are
very different.  The kernel's scheduler determines which *processes*
are to be run at each moment on the system.  You can see the processes
being scheduled and run via top, or better yet, atop; you can see how
the processes all relate via pstree.  As an example of these processes,
I started the mutt program to read this email by typing the command mutt
into a bash shell prompt; that process, the bash shell, read the command
and created a new process from the mutt program, which then allowed me
to read the email.  To answer the email, mutt started the vim editor,
allowing me to type this response you are now reading.  Those are example
of the various processes.

The job scheduler determines which *jobs* are to run; jobs are a sequence
of commands that you want to run, likely composed of many processes
as described above.  Once the job scheduler launches the job, the running
of the individual processes is controlled by the kernel's scheduler.

David N. Lombard, Intel, Irvine, CA
I do not speak for Intel Corporation; all comments are strictly my own.

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