User space scheduling

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!

Rob

---------------------------------------------------------------- Robert Kaiser email: rkaiser@sysgo.de SYSGO AG Am Pfaffenstein 14 phone: (49) 6136 9948-762 D-55270 Klein-Winternheim / Germany fax: (49) 6136 9948-10