Re: L4_ThreadSwitch behaviour

[Martin Christian]
> My question is related to both L4Ka::Pistachio and
> NICTA::Pistachio-embedded, thus I'm mailing to both lists.

> Consider the following test cases:

> Case A
> ======
> 1. The root thread creates a new thread in a new address space (AS):
> 2. The root thread "refills" it's time slice (maybe that's bogus, but it
> is meant to ensure a full time slice is donated): L4_Yield();
> 3. The root thread donates the rest of it's time slice to the new
> thread:
>    L4_ThreadSwitch( ping_tid );

> Case B
> ======
> 1. The root thread creates a new thread in a new AS
> 2. The root thread waits for a startup IPC from the new thread (of
> course, the new thread has to be altered to send such an IPC)
> 3. The root thread "refills" it's time slice
> 4. The root thread donates the rest of it's time slice to the new thread

> Problem:
> Case A won't work, but Case B does. For Case A the new thread won't run,
> even though it's active and in the ready queue. The only difference is
> that in Case B the pages which hold the code are already mapped in the
> new threads AS.

A bit late for me to jump in, but I'll do it anyway.

As you've already been told, doing scheduling purely based on
timeslice donation is not a very good idea.  Even if you manage to
donate almost a complete timeslice there is no telling how much of the
timeslice you'll manage to consume due to interrupts, exception
handling, etc.

In your case I suspect that handling the page faults in the new thread
will consume quite a bit of your timeslice.

	eSk