User space scheduling

Robert Kaiser rob at
Tue Jan 21 16:03:06 CET 2003

Hi experts,

I am trying to identify (and examine) ways to implement user-level scheduling 
on L4.

I read in Michael Hohmuth's diploma thesis on L4Linux that it would have been 
desirable to use the preemption handlers to implement Linux's scheduling 
policy, but since L4 did not support them at the time, he used L4's built-in 
scheduler instead.

Also I read a posting by Gernot Heiser in the mail archive of this list in 
which he suggests that the preemption handler concept is somehow flawed.

To my knowledge, none of the current L4 variants has implemented the concept.

To be honest, I'm having difficulty to fully understand the concept. For 
instance, the difference between an internal and an external preempter is not 
clear to me.

So my questions are:

- is there any further reading (besides the L4 Reference Manual and the L4
  User Manual) that describes the concept ?

- has the concept actually been put to the test ?

- roughly, how would I implement a specific scheduling policy in e.g. L4Linux
  based on this concept (assuming L4 does provide it) ?

Thanks in advance for any insights!


Robert Kaiser                         email: rkaiser at
Am Pfaffenstein 14                    phone: (49) 6136 9948-762
D-55270 Klein-Winternheim / Germany   fax:   (49) 6136 9948-10

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