Instances of lazy scheduling and timeslice donation in L4 implementations
Udo A. Steinberg
us15 at os.inf.tu-dresden.de
Tue Jan 24 21:34:29 CET 2006
On Tue, 24 Jan 2006 19:54:29 +0100 Espen Skoglund (ES) wrote:
ES> Speaking for the Pistachio implementation: The time is accounted to
ES> the thread who currently "owns" the timeslice (thread A in this case).
ES> Each time a timer tick occurs, and there are no preemptions by higher
ES> priority threads, thread B will run on the time donated by thread A.
ES> This is according to the spec.
So far all is clear.
ES> Once the timeslice expires a new
ES> scheduling decision is made. This may or may not cause thread B to
ES> continue running (depending on priorities, scheduling queues, etc.).
This is also clear.
The tricky case is as follows:
1) A performs a thread_switch syscall, donating its time slice to B
2) B executes and consumes part of A's time (but not all)
3) B is preempted by a higher-priority thread H
4) H blocks
How does B get to consume the remainder of A's time slice, i.e. the part
that it did not use up in 2) ?
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