[no subject]

[John Yau]

>Your mechanism is basically "backboost". Its how you get X to keep a
>high piroirity, but quite unpredictable. Giving a boost to a process
>holding a semaphore is an interesting idea, but it doesn't address the
>X problem.

Hmm...I'm actually curious why you called it "backboosting".  In academia
this approach first described in the paper here:

L. Sha, R. Rajkumar, and J. P. Lehoczky. Priority Inheritance Protocols: An
Approach to Real-Time Synchronization. In IEEE Transactions on Computers,
vol. 39, pp. 1175-1185, Sep. 1990.

is referred to as priority inheritance.  Is there significant difference
between your implementation and priority inheritance schemes implemented in
other OSes?  If so, why backboosting?

I was under the impression that pipes and IPC in general are synchronized
using some sort of semaphores/mutex...or does Linux use a different
mechanism for IPC and does away with user space synchronization all together
(e.g. flip-flop buffers with the kernel arbitrating all contention)?  IIRC
processes don't write to X directly and has to send data to X via IPC.  If
some futex derivative is used to synchronize the producers with X, then
making priority inheritable futexes would solve the problem.

>The scheduler in Linus' tree is basically obsolete now, so there isn't
>any point testing it really. Test Con's or my patches, and let us know
>if you're still having problems with sir dumps-a-lot.

Okay enough said, you and Con should get your patches merged into that tree
ASAP if they're ready.


John Yau
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