Note that the Inside L4 document refers to the old MIPS kernel, which is one implementation of (and extended) V2 API.
It also, like many other implementations, does time-slice donation incorrectly (i.e. blindly). Time-slice donation should respect priorities. I believe that this is fixed in NICTA::Pistachio-embedded, but the code is the ultimate reference ;-)
Gernot
On Fri, 20 Jan 2006 20:21:32 +1100, Sergio Ruocco sergio.ruocco@nicta.com.au said:
SR> According to Gernot's "Inside L4/MIPS" Version 2.19 of January 30, 2001 SR> https://www.ertos.nicta.com.au/publications/papers/Heiser:IL4.abstract.pml
SR> Section 2.1.2 (page 7): SR> Time-slice donation can happen in one of two ways: SR> � explicitly via the thread switch system call. This call donates the SR> remainder of the caller�s current time [...] SR> � implicitly via IPC. IPC operations are often accompanied by a context SR> switch from the sender to the receiver, in which case the sender�s SR> current time slice is implicitly donated to the receiver.
SR> and
SR> Section 5.2.3: SR> " The other point to note is that, while the sender thread is put into SR> the busy list to allow it to be scheduled again, the context switch to SR> the receiver is actually performed without any scheduling (lazy SR> scheduling [Lie93]). The receiver simply continues in the remainder of SR> the sender�s time slice. This is an instance of time-slice donation in L4."
SR> I assume that the above described cases still hold for most, if not all, SR> the current L4 implementation(s). The IPC time-slice donation is a SR> classic optimisation, and ThreadSwitch() is part of the L4 specification.
SR> I have few Qs:
SR> 1) Besides the ones above, are there in the current L4 implementations SR> other instances of: SR> 1.1) time-slice donation ? SR> 1.2) lazy-scheduling ?
SR> 2) If yes, do they affect or are affected in special ways by [kernel] SR> interrupt threads ? SR> (I think not, but with implementation/optimisations you never know...)
SR> Thanks
SR> Sergio
SR> --
SR> --
SR> http://www.cse.unsw.edu.au/~sruocco/ SR> ERTOS Researcher Lecturer SR> National ICT Australia Ltd. University of New South Wales
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